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SARS-CoV-2, the virus that causes Covid-19, can float in the air. In particular, it can linger in poorly ventilated indoor spaces, spreading farther than 6 feet from its source. These indoor public spaces are high risk and should be avoided while the virus is still spreading.

But, increasingly, people are returning to those spaces: Bars and restaurants are operating in limited capacity in some places, and are fully reopened in others. Some schools and universities have resumed in-person classes, and mayors are allowing some live entertainment venues to host events.

With the weather growing colder, experts fear indoor gatherings in these and private spaces could spark new outbreaks. Already, cases are increasing nationwide, and experts are growing more concerned about a potential fall-winter Covid-19 surge.

To make indoor communal spaces safer, experts keep stressing that they need to be “well-ventilated.” But what does that mean? In conversations with several air quality experts and engineers, I found ventilation to be simple in concept and potentially fraught in execution.

“It’s a huge engineering problem,” Shelly Miller, an environmental engineer at the University of Colorado Boulder, says. “We don’t have the systems in place for many buildings to be operated appropriately during a pandemic.”

As Derek Thompson observes in the Atlantic, a lot of places have put on a big show about cleaning surfaces — what he calls “hygiene theater” — though surface contamination is not thought to be a large source of Covid-19 transmission.

Making places safer, instead, should mean improving air quality. But “have you ever heard a restaurant reopening announce they’ve improved ventilation or increased ventilation?” Lidia Morawska, an engineer and the director of the International Laboratory for Air Quality and Health at Queensland University of Technology, recently told me. “No.”

Ventilation concerns are not limited to restaurants and schools. Recently, a report from the University of California San Francisco noted “exceedingly poor ventilation” at the San Quentin State Prison, which saw a huge outbreak of more than 2,200 cases.

Ventilation efforts could easily fall into the “hygiene theater” trap if not done well. So here’s a guide for how to think about safer — but not necessarily “safe” — indoor air, and all the hurdles that may get in the way. We need to think about controlling the source of the virus indoors, about mixing more outdoor air with indoor air, and about air filtration and cleaning devices.

The experts I spoke with agreed: We can’t ventilate and air purify our way out of the need to wear masks, reduce occupancy in indoor spaces (or just avoid many of them all together), and physically distance. The indoor space that can’t enforce these measures, or allow activities that involve mask removal — like bars and restaurants — probably shouldn’t be open. And, still, the most important way to make indoor spaces safer is to decrease community Covid-19 spread as much as possible. It may not be easy for all spaces to achieve ideal ventilation.

There are no perfectly safe indoor environments during the pandemic, but there are clear goals to have in mind when trying to make them safer with ventilation. Here’s where to start.

First: Limit the amount of virus in the air in the first place

Intuitively, I think we all know how to think about cleaning surfaces: Wipe them down with a disinfectant, or scrub with good old soap and water. Cleaning the air is an entirely different challenge. You can’t just spray it with chemicals and call it a day.

“Cleaning the air is at least as important as cleaning surfaces, but you do it very differently,” says Linsey Marr, a Virginia Tech engineer who studies the airborne spread of viruses. “We end up having to breathe whatever it is we spray. And if it’s harmful to the virus, it’s likely it’s also harmful to us. So we need to take a totally different approach.”

There are other challenges to cleaning the air, too. One big one: Floating particles can move. If you clean one section of air in a space, new dirty air can move in and replace it. Also, air cleaning needs to be continuous in the spaces we inhabit. As long as there are living, breathing people in a space, we’re potentially contaminating it with virus.

The first thing to do in thinking about cleaning the air, says Jeffrey Siegel, an air filtration expert at the University of Toronto, is to think about limiting the source of the contagion in the first place (i.e., living, breathing people). There’s an old saying in his line of work: “If you’ve got the odor of manure, don’t try and ventilate to get rid of it, get rid of the manure,” he says. “That’s the exact idea, right? Get rid of the source or manage that source.”

SARS-CoV-2 gets into the air via human breath. So we should start by reducing the number of humans in a space, masking those who have to enter, and limiting activities like singing or shouting that can propel even more virus-laden particles into the air.

From contact tracing studies, we know the virus spreads most readily through close contact, with the risks increasing with the amount of time spent in close proximity. However, there are some situations in poorly ventilated indoor spaces where the virus may be able to float in the air for an extended period (tens of minutes or more), or spread in a gaseous cloud over an area larger than 6 feet (some of that long-range floating virus may still be able to infect people, some of it may not). Ventilation may help decrease the chances of transmission in these indoor environments.

“Ventilation may be able to help reduce indoors transmission, but it’s never going to be as effective as simply not having lots of people in a single indoor space,” Boston University epidemiologist Eleanor Murray says in an email. “If a workplace can function with employees working remotely, then it will be safer for them to do so than to have all employees come back to work even with better ventilation. But there may be a few employees who would be better served by being at the office, and for those, improving ventilation will help make the office as safe as possible.”

Second: Ventilate

Outside of source control, there are three basic ways to clean the air and reduce the concentration of airborne virus. The first is to simply ventilate, or increase the amount of outdoor air in indoor spaces, and to make sure the inside air is replaced by outside air several times per hour.

“So the air in your home probably changes over once every hour or two hours,” Marr says. “We’re aiming for an air exchange rate of, like, six per hour.” That recommendation, she says, comes from studies of tuberculosis transmission. (Tuberculosis is not SARS-CoV-2. TB is much more contagious and is thought to be able to spread farther and stay longer in the air.)

It’s important to remember, too, that scientists still don’t really have a specific figure on what amounts to a dangerous, infectious concentration of virus in the air. “There’s no perfectly ‘safe’ level of ventilation because we don’t actually know what ‘safe’ is, since we don’t know how much exposure leads to transmission,” Angela Rasmussen, a Columbia University virologist, says in an email.

Six air changes an hour is a baseline. “If you want the risk down to zero, you’ve got to get to an infinite number of air changes per hour,” Marr adds. Which is impossible.

Again, more ventilation may be “safer,” but it’s not “safe.”

The easiest way to increase ventilation: open windows. This will increase the amount of outside air (which does not have virus in it) coming in to dilute indoor air (which may have virus in it). The less concentrated the virus is in the air, the less likely it is to infect people.

It seems simple, but it’s not foolproof. There are some specific scenarios where opening windows can be counterproductive and yield unpredictable effects, as Siegel explains.

Let’s say you have a bathroom. It would be a good idea to keep the bathroom air in the bathroom. After all, many types of viruses can spread in bathrooms, and in the case of Covid-19, it’s possible for the virus to be sent into the air via toilet flushes (though it’s less clear if someone can be infected this way). So it’s ideally best to not let that bathroom air get out into other spaces.

To keep the air in the bathroom in the bathroom, it needs what engineers call “negative pressure,” meaning that air can flow into the bathroom but not out.

“And then you open a window in the room beside the bathroom,” Siegel says. “And once you open windows, you give up on any idea of controlling pressurization or depressurization.” When this happens, the potentially contaminated air in the bathroom will start flowing out.

The point of this example isn’t to make people scared of opening windows. It’s just that indoor spaces are complicated, and airflow can be hard to predict.

“No one I know — even some of the best building modelers in the world — can accurately model a building with open windows,” he says. “It’s just way too dynamic of a system. We know that, in general, ventilation rate increases. And I’m not going to tell anyone not to open the windows. But really we can’t tell you what it’s doing to airflow in the space.”

This is one of the potential pitfalls with ventilation: “Ventilation pathway matters too,” Siegel explained on Twitter. If a fan meant to increase ventilation ends up blowing virus across people’s faces, it’s self-defeating. This is what’s believed to have happened in a restaurant in China, where people sitting in the path of an air conditioning fan got sick. Later, researchers also said that the restaurant A/C system pulled in no outdoor air, and the air in the restaurant wasn’t replaced even once in an hour, let alone six times, which likely contributed to the outbreak there.

How to monitor ventilation

So how do you know if you’re doing ventilation right? Is there any way to monitor your airflow and know the air exchange rate? Here, things get tricky. One indirect way to do this is to purchase a carbon dioxide detector (which are around $100 online) to give you a rough sense of air quality. When we exhale, we exhale CO2. “How much CO2 is in an indoor space is basically a metric of how much air other people have expelled in that space,” Jose-Luis Jimenez, a chemistry professor at the University of Colorado Boulder, says. So high and rising CO2 levels in a space can be a sign it’s not properly ventilated.

“The relationship between CO2 and outside air ventilation is really complicated and not something I’m advocating the public try to figure out,” Miller says. But, as a general benchmark, the average C02 concentration of outdoor air is around 400 ppm (parts per million). So indoor spaces should ideally have a CO2 concentration of under 500 or 600 ppm in a room where people are breathing. That will tell, roughly, whether outdoor air is being mixed with indoor air at a reasonable level.

Building managers, though, shouldn’t depend entirely on a CO2 monitor. Again, it’s an indirect measure. If there are only a few people in a space, they may not generate enough CO2 to make the sensor rise that much even in a stagnant environment. And it only takes one person to start an outbreak.

(There’s also some room for commonsense measurements, too: Use your nose. If you can smell odors wafting through a building coming from indoor sources, the space may not be adequately ventilated. “If you walk into a place and it feels stuffy and the windows aren’t open, then that’s an indicator that there’s not good ventilation there,” Marr says.)

In commercial settings, some building operators might be able to adjust the amount of fresh air pumped into a building’s ventilation system. During the pandemic, they should do this. But, as Miller explains, “many [commercial HVAC] systems don’t run on 100 percent outside air.” It’s too energy-intensive. “You can’t provide air conditioning and heat with 100 percent outside air,” she says. So, in some cases, there is a limit to how much outside air an HVAC system can mix into a building.

Other systems might be in disrepair and unable to ideally ventilate buildings, even if their systems are cranked up. Particularly in schools, ventilation systems can be old and in disrepair. In June, the Government Accountability Office published a survey of 65 school districts that receive aid from the federal government. It found 41 percent of the districts needed to update HVAC equipment in half of their schools. Separately, in New York City, a Daily News investigation found that “roughly 650 of the 1,500 buildings surveyed in 2019 by city inspectors had at least one deficiency in their exhaust fans.”

A huge part of the challenge of increasing ventilation is that different buildings, built in different eras for different purposes, will need potentially different solutions. Older buildings might not have any central HVAC systems at all. And some with HVAC systems may operate well for some rooms but less well in others.

“When I think about my daughter’s school,” Siegel says, “I don’t worry about the school as a whole as much as I worry about that classroom where they can’t open the windows because there’s a construction site right nearby.”

It’s important to know here that ventilating schools has benefits that are broader than its pandemic applications. Kids need to breathe healthy air (the dangers of air quality for children’s’ health and cognitive well-being are as clear and critical as ever). And allowing them to do so will require huge investments.

“We can’t even get the Congress to allocate, you know, $600 a week in unemployment, let alone a billion dollars to schools to upgrade their HVAC,” Miller says.

“We have systematically neglected our HVAC systems for a very, very long time,” Siegel says. “Schools are one classic example of that. But also every building. And so now all of a sudden, we’ve got a pandemic, and we say, well, we want to increase ventilation … you don’t get there without some amount of investment.”

(Hospitals, you might be curious to know, already have extensive requirements in place for ventilation. So which comes at a great cost and takes lots of energy to use.)

Air filters can work too — if used properly

The goal in ventilation is to replace potentially virus-laden air indoors with virus-free air. One way to do this is to bring more outdoor air inside. But this isn’t always doable. You can’t easily open windows for ventilation when there’s a lot of hazardous pollution outside (like wildfire smoke). So, the other way is to filter the indoor air itself.

This also is simple in theory, but the implementation can be tricky.

It starts with getting a good air filter. For this, the American Society of Heating, Refrigerating, and Air-Conditioning Engineers suggests using filters with a MERV-13 designation or higher. Or use a portable HEPA filter (there are some DIY versions you can try on the cheap).

MERVs are based on a filter’s performance in filtering out particles between 0.3 and 10 microns. SARS-CoV-2 could very well be found in respiratory droplets in this size range; the higher the MERV number, the higher the probability that the filter will remove these droplets.

HEPA filters, more common in portable air filters, are slightly different. The “HEPA” designation means they filter out at least 99.97 percent of particles that are 0.3 microns. Which is to say, they filter out practically everything. (A quirk of the physics of filtration is the very smallest particles are actually easier to filter out than the 0.3 micron ones. The smallest particles get pushed toward filter fibers because of their collisions with gas molecules in the air, Siegel explains.)

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But installing higher-quality filters isn’t enough.

“I can’t just tell you in good conscience, ‘This is the filter you should use to protect against Covid-19 transmission,’ because it really depends how you use that filter,” Siegel says. “We much more often have an implementation problem than a lack of technology problem.”

Often, he says, in buildings, a filter will be improperly sealed so that some unfiltered air sneaks past it and recirculates in the building; this downgrades its filtering ability. Also, not all systems can run these higher-efficiency filters, which can be quite dense. They often require more powerful fans to push air through.

For instance, Siegel says that, typically, home window AC units don’t operate with very powerful fans. So if you put a good filter in the unit, “you would not move any air, your air conditioner would cease to perform as an air conditioner, the coil would ice up very rapidly, and you’d have a nice block of ice with no air blowing across it.”

The other consideration: These higher-quality filters need to be replaced more frequently as they “fill up” with more stuff more quickly and it becomes harder to push air through the filter. Also (this list of caveats and considerations is getting long, right?) you need to buy a unit that’s sized correctly for the space you are in. The filtering unit should ideally, along with ventilation, lead to six or more air exchanges per hour.

“You want something that’s good for the size of your room or bigger; bigger will give you better cleaning power,” Marr says. “But, you know, even if you get something that’s smaller, it’s not going to harm you.” She adds that you also need to be careful when changing the filters because they could be contaminated with virus.

And finally: Air filters have to be constantly running to work.

“Forced air systems [like centralized heating and cooling] in most residential contexts and in some commercial context only come on when there’s a need for conditioning,” Siegel says. That is, they only turn on when it gets too cold or too hot. For a filter to work at its best, air needs to be constantly running through it. Some systems may need to be tinkered with to get this to happen.

Again, it’s hard to know, exactly, what impact air purifiers will have on transmission. “My main concern with these ventilation systems is that we do not know really whether they will decrease transmission risk substantially,” Muge Cevik, a physician and virology expert at the University of St. Andrews, says in an email. After all, there aren’t randomized controlled studies of using air cleaners during this pandemic to decrease transmission.

In theory, air purifiers should help. “It’s not rocket science,” Jimenez, who strongly advocates for their use, says. “If you pass air through the filter, it will catch the particles.”

Watch out for snake oil air-cleaning products

There’s yet another option for removing virus from the air: killing it with ultraviolet lamps. That said, Miller — who specializes in studying devices that do this sort of thing — doesn’t recommend these for the average consumer.

“While they can be effective, there is not enough testing/certification for these devices,” she says. “These are pretty complex, and there are a lot of great applications and some really good companies that can help with design and install.” But, she says “there are also a lot of bad lamp manufacturers and people selling devices that don’t work. Best left to engineers and reputable companies to support these installations.”

If you look at air cleaning products, you’ll find a lot of gimmicks: ionizers, plasma generators that claim to amp up the power of filters. “There’s very little science behind them,” Siegel says. “It’s not only that the devices are ineffective and maybe lull people into a false sense of security, but in some cases they’re actually harmful.”

Watch out, in particular, for machines that can generate ozone. Ozone is a pollutant that can interact with a lot of different products in your home and create harmful chemicals to breathe in. “It reacts with carpets and skin oil and all kinds of things inside of buildings,” Siegel says, “forming all kinds of harmful byproducts, ultra-fine particles, formaldehyde, all kinds of other things that we would worry about indoors.”

So stick with HEPA or MERV-13+ rated filters. Or just open windows.

Remember: Hygiene theater is possible when it comes to air quality as well. If a school or any indoor space says it has improved ventilation, ask how. Marr suggests asking building operators what the air exchange rate is (if they don’t know it, maybe be wary about the space). Ask about what filters have been put in place. Ask if their HVAC systems have been routinely maintained.

“Even if you can’t reach the target — six air changes per hour — if you can improve, that will still be helpful,” Marr says. “Do what you can, because that will reduce the risk of transmission. Don’t give up.”

We need to invest in cleaner air, period. Pandemic or not.

There are no risk-free situations in a pandemic. Again, good ventilation needs to take place alongside other precautions. The hope is “if we can take this whole suite of stopgap measures from the ventilation standpoint and add it to masks, social distancing, reduced occupancy, limited time indoors, the whole package could reduce our risk substantially to help get the case rates down,” Miller says.

This is particularly important heading into the fall and winter seasons, when more people will be spending more time indoors in potentially risky environments.

Experts also worry that the US Centers for Disease Control and Prevention is not being helpful enough in its air quality recommendations. For instance, the CDC recommends that schools “ensure ventilation systems operate properly and increase circulation of outdoor air as much as possible, for example by opening windows and doors.” But they don’t even weigh in on the merits of putting a HEPA air purifier in each classroom.

“It would carry more credibility,” Jimenez says, if the CDC would discuss their use rather than leave the conversation in the hands of independent scientists speaking for themselves. “When I was talking to a school district, they were all saying, ‘Well, the CDC doesn’t recommend air cleaners.’” In Jimenez’s mind, air cleaners are essential. But it’s hard to get the message across without a huge institution like the CDC echoing it.

So much of the pain of the pandemic builds on preexisting problems. Too many schools and other buildings have overlooked their ventilation and indoor air quality to begin with. Addressing ventilation can’t just be a one-time Band-Aid during the pandemic. It’s an investment. And not just for future pandemics but for our overall health.

“The best possible case is that you reduce risk of Covid-19 and you make your indoor air quality better,” Siegel says. “The worst possible case is that you make indoor air quality better but don’t appreciably change Covid-19 risk.”

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If Joe Biden beats Donald Trump this November and ends up in the Oval Office in January, he’ll quickly face one of the gravest challenges any president has seen in the modern era: Hundreds of thousands of Americans will be dead from Covid-19. Public trust in scientific and government institutions will be depleted. If the fall and winter goes as badly as some experts fear, coronavirus outbreaks may be at a new peak. And if a vaccine gets approved, it will still need to be distributed to hundreds of millions of Americans quickly and equitably.

Biden’s immediate job would be fixing the mess left behind by his predecessor — one that’s left America with one of the worst coronavirus outbreaks in the world and, as of September, more daily Covid-19 deaths than all but two developed countries.

Experts say these problems are fixable, but fixing them will largely come down to political will. The policy solutions are things that we’ve all heard about throughout the pandemic: aggressive testing and tracing to contain new outbreaks. Mask-wearing to slow the spread of the coronavirus. Economic support for those affected by the epidemic, at once providing financial support and making social distancing more feasible.

“It’s not rocket science. It’s not that we need some new thing that hasn’t been thought of before,” Jen Kates, director of global health and HIV policy at the Kaiser Family Foundation, told me. “There are things that have been done in some cases, or can be done. But if there was a stronger, coordinated federal role … that could really make a difference. It’s happened in other countries.”

Another part of Biden’s job will be to, in effect, repair Americans’ trust in science — bolstering public health institutions like the Centers for Disease Control and Prevention (CDC) and the Food and Drug Administration (FDA), widely considered the gold standard of public health agencies in the world before the pandemic.

Biden will also have to prepare the country for the rollout of a coronavirus vaccine that could take months if not years. The challenge here isn’t just discovering a safe and effective vaccine; many experts, in fact, are hopeful the world will do that by the end of 2020. The difficulty will be figuring out how to quickly produce and distribute up to hundreds of millions of doses of the vaccine to the general public — an unprecedented effort. That will also require persuading the public to take the vaccine, which could be particularly challenging coming off the heels of a highly contentious presidential election.

Biden, for his part, has vowed to do much of this. His website promises to adopt a masking mandate and boost testing and tracing. His campaign has vowed to “listen to science” and “restore trust, transparency, common purpose, and accountability to our government.” And he’s promised to “plan for the effective, equitable distribution of treatments and vaccines.”

Trump could do all of this, too. But there’s very little faith among experts that Trump will change his current approach to the pandemic, especially if he wins reelection. Instead, he’ll likely continue doing what he’s done: deliberately downplaying the pandemic, demanding states reopen far too quickly, punting testing and tracing to local and state governments with more limited resources, mocking masking, and continuing to try to politicize the CDC and FDA.

That failed response helps explain the US’s current Covid-19 outbreak, leading the country to more than 200,000 deaths from the disease — by far the highest recorded death toll in the world. When controlling for population, the US hasn’t had the highest death rate for Covid-19, but it’s among the top 20 percent for developed nations, and has seven times the death rate as the median developed country. If the US had the same Covid-19 death rate as, say, Canada, more than 120,000 more Americans would likely be alive today.

That damage can’t be reversed. Those 200,000 deaths are on the US’s record forever. But Biden, at least, could take actions that would help prevent America’s outbreak from getting even worse.

1) Implement policies we know work: Testing, tracing, masks, and social distancing

There are problems in the world with really difficult or unknowable answers. That’s not as true for Covid-19: While there’s a lot about the coronavirus we’re still learning, there are many policy approaches that we know work and the US hasn’t really embraced. This is, then, more a matter of will than knowledge — which is something that Biden, especially if he has a sympathetic Democrat-controlled Congress, could address.

Testing is among those proven policy approaches. When paired with contact tracing, more testing can help public health officials detect outbreaks, get the infected to isolate and the infected’s close contacts to quarantine, and use broader public health measures as needed. This is an approach that has worked well in many other developed countries, from Germany to South Korea to New Zealand.

The US, however, has struggled to build up its testing capacity. It’s made big improvements since the start of the pandemic, but testing hasn’t increased above 1 million tests a day — far lower than experts say is needed, given the country’s large epidemic overall. As a result, the percentage of tests coming back positive, which experts use to measure testing capacity, stubbornly remains at 5 percent or more; it should be, experts suggest, far below 5 percent and preferably below even 3 percent. It can still take days to get test results back, and that can spike to weeks if demand, due to a new outbreak, is high.

According to experts, part of the problem is the US never fundamentally fixed supply line problems — with shortages popping up for swabs, reagents, testing kits, and other needed equipment throughout the pandemic. There was also an economic disincentive to building out capacity too much: If a lab, for example, massively scales up its coronavirus testing, but the pandemic is over in a few years, it will be left with a lot of infrastructure it doesn’t use or get revenue from, a huge money sink.

A Biden administration could address these problems, using the powers of the federal government to coordinate the supply line, maintain its stability, and guarantee that any businesses and organizations will be made whole for investments into coronavirus testing. To do all of that, the country needs a national plan — which it currently lacks.

There’s a chance the supply problem fixes itself. With the development and mass production of new antigen tests that don’t have to go through a lab and hospitals, Americans could get access to many more tests that also return results within minutes instead of hours or days. Compared to the hold-ups with the current PCR tests that go through labs or hospitals, it would be a welcome change.

Still, there would be remaining questions about how to deploy and distribute those new tests based on equity and need — questions that a national plan could address.

After that, the US would still face another problem: how to actually use those tests. That’s where contact tracing comes in, as “disease detectives” track down newly infected people and their close contacts to convince them to isolate and quarantine. Earlier this year, Crystal Watson, senior scholar at the Johns Hopkins Center for Health Security, projected that the US would need at least 100,000 contact tracers. She estimated the US still has fewer than half of that number.

Since Watson’s original estimate, Covid-19 outbreaks in the US have also gotten much worse and more widespread. That presents two major problems: First, the US now needs even more contact tracers than she originally estimated. Second, it’s now likely impossible for contact tracing to really bring down the epidemic on its own, because there are just way too many cases for even a massive team of tracers to track down and contain.

So while a large federal investment in a contact tracing workforce and equipment could help, it probably won’t be enough. “We really have to take other measures to bring down transmission in order for contact tracing to be effective,” Watson told me.

Among the other measures: masks. The scientific evidence for masking has gotten much stronger since the start of the coronavirus pandemic, with multiple studies linking the widespread use of masks and new mask mandates to drops in Covid-19 cases and deaths. One study in Health Affairs suggested that, with caveats that this is just an approximation, “230,000-450,000 COVID-19 cases may have been averted on the basis of when states passed these mandates.” If mandates were nationwide instead of left to a minority of states at the time, it stands to reason the impact would have been much bigger.

Whether the federal government could impose a mask mandate on its own gets into legally dicey territory. But a Biden administration and Congress could use financial incentives to encourage cities and states to adopt masking mandates and provide extra resources to enforce them. That could get the remaining 16 states without a mask mandate, or at least some of the municipalities in those states, to adopt the policy.

Just having a president who is unequivocal about the benefits of masking and consistently wears a mask in public, experts claimed, would also signal to the rest of the country that this is the right thing to do. It’s “just the public image of a responsible adult doing what they’re supposed to do,” Cedric Dark, an emergency medicine physician at the Baylor College of Medicine, told me.

Even with all these measures in place, the US will have to continue social distancing to some degree. No one wants this, but, depending on how bad fall and winter outbreaks get, some cities, counties, and states may have to bring back lockdowns.

The federal government can provide clearer guidance on how and when to do this. It can also, with Congress’s backing, pass legislation that financially supports people affected by lockdowns. A commonly cited idea is a bailout for bars, restaurants, and other businesses, which would not only help keep these employers and their employees afloat but make the negatives of closing down much more tolerable and, therefore, make closing down easier and more likely if it’s deemed necessary to fight the coronavirus.

Ultimately, this could benefit the economy by mitigating the need for such harsh social distancing efforts. A preliminary study from the 1918 flu pandemic found that cities that took more aggressive action against outbreaks back then emerged stronger economically. Germany and others have similarly seen their restaurant businesses recover by controlling the coronavirus. As Watson put it, “In order for our economy to recover, we really do need to resource our public health response more effectively.”

Again, none of this is really new. The experts I spoke with often joked that we were having the exact same conversations now that we had back in the spring and summer. But the US hasn’t fully committed to these kinds of policies — and a Biden administration could.

2) Rebuild trust in science and public health institutions

Under Trump, and particularly throughout this pandemic, trust in many institutions has dwindled. This has applied even to American institutions that were in the past considered the best of the best in the world for public health, such as the CDC and FDA.

The country needs “a long campaign to get people to trust science again,” Dark said. “My colleagues don’t trust anything coming out of the CDC now, due to how politicized it’s been.”

A report from the Covid-19 Consortium for Understanding the Public’s Policy Preferences Across States, based on a 50-state survey on Covid-19, captured the trends: Across the country, trust in “doctors and hospitals,” “scientists and researchers,” and especially the CDC has fallen. Trust in all of these is still relatively high — much higher than trust in either Biden or Trump — but it’s a concerning trend. Among different political and demographic groups, trust can be even lower, too.

“Six months ago, the FDA and CDC were shorthands for gold-standard scientific advice,” Ashish Jha, dean of the Brown University School of Public Health, told me. That’s changed, he lamented.

Some of this reflects genuine failures by these institutions. The CDC and FDA both played roles in the US’s testing problems — the CDC by botching its tests, and the FDA dragging its feet in approving more testing from private and independent labs — leading to what’s been widely called a “lost month” for testing in February. The CDC was also slow to recommend masks, then failed to admit to messing up and explain its about-face on the issue. The FDA, meanwhile, has acted in ways that seem politically motivated rather than based on rigorous evidence, such as when it allowed, before warning against, hydroxychloroquine, which was always unproven but Trump spoke favorably about.

Although the CDC and FDA are supposed to stand above partisan politics to help maintain their credibility, Trump and his administration have actively meddled in their affairs and work. Trump and his political cronies have, for example, repeatedly pushed the CDC to do things solely to support Trump’s unproven claims about Covid-19 — forcing the agency to briefly recommend less testing, loosen its guidelines for reopening, and delay studies that contradict the president. All of that has called into question just how independent the CDC truly is.

Fixing this will take time, but it’s fairly straightforward: Biden and the political actors in his administration should back off, allowing scientists to take a leading role in these agencies and the US’s Covid-19 response in general.

Carlos del Rio, executive associate dean of the Emory University School of Medicine, put this simply: “Pay attention to science. Let the science guide the response, not the politics.”

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That includes giving these institutions control of the public messaging. While Trump appointed Vice President Mike Pence to lead the White House’s coronavirus task force, Biden could put a scientist or public health official in charge. While Trump sidelined the CDC after Nancy Messonnier, director of the CDC’s National Center for Immunization and Respiratory Diseases, warned in February that “disruption to everyday life might be severe” due to Covid-19, Biden could allow the agency and its experts to speak plainly and truthfully to the public.

That should also translate to the policy level. When the CDC makes recommendations, the Biden administration shouldn’t, as Trump has, undermine the guidelines or force the agency to change them. When scientists are recommending a pivot in the country’s approach, that should be seriously considered, even if it contradicts what the administration said or did in the past, while clearly and transparently explaining why a change is needed.

“The CDC has the expertise to lead us in this pandemic,” Jorge Salinas, an epidemiologist at the University of Iowa, told me. “We just need to ask them.”

The idea is to prove to the public time and time again that the country’s response to Covid-19 isn’t driven by politics but by science. It’s an admittedly difficult task for a country that’s consumed by politics and polarization at every level, but it’s something, experts said, that’s simply necessary to improve America’s response to the coronavirus.

3) Prepare the country for a months-long rollout of a vaccine

If we get a little lucky, there’s a chance that the world will finally have a proven, safe, and effective coronavirus vaccine by the end of the year. It would be an incredible achievement — the fastest turnaround on a vaccine for a major disease in human history.

But that won’t be the end. After a vaccine makes it through the last rounds of research necessary to get FDA approval, it’ll have to be distributed to potentially more than 300 million people in the US alone. Given that some of these vaccines will require two doses, that means manufacturing hundreds of millions of doses of the medication — something that the country simply hasn’t done at the scale and speed that the pandemic demands.

There’s already a lot of work, from both governments and private actors like Bill Gates, to manufacture all those doses. It’s possible, even likely, that the current work isn’t enough — and that will demand more action and more funds by a Biden administration.

After that, there will be tough questions about who gets priority. There’s a consensus that first responders and health care workers, at least, should get a vaccine first. Beyond that, there are genuinely difficult questions: Should older adults get priority because they’re more vulnerable? Should essential workers? What about younger people, who seem to be behind the country’s most recent large outbreaks? “It gets complicated,” Jha acknowledged.

Another element will be persuading the public to actually take a vaccine. If a vaccine is 50 to 70 percent effective, as appears likely at first, experts argue that close to 100 percent of the population will need to take one to reach true herd immunity. That will be a tall order as the country deals not just with traditional, unscientific anti-vaxxer sentiments but also more nuanced concerns about whether the current politicized, fast process coronavirus vaccines are going through can really test adequately for safety. Different surveys have found a third to half of Americans don’t plan to or don’t know if they’ll get a coronavirus vaccine.

“It does seem like there has been less of a push to actually come up with a really good communications plan,” Watson said, “but also to just have a general dialogue with people as you go along about what the process has been like for creating a vaccine, what standards have been upheld, and the results of the safety and efficacy trials.”

Breaking through those concerns will require research and surveys to subsequently build a massive communications campaign that will try to push people to get vaccinated. This will be a huge undertaking, and it might not even work, depending on if a new administration can rebuild trust in science and depoliticize its public health institutions.

All of this could take a long time. Experts were unanimous in arguing that getting a vaccine by the end of 2020, should that happen, won’t be the end of the pandemic. They said that getting a vaccine out there could take at least months. Some spoke in terms of years, well into 2022 or 2023. “President Biden and Vice President [Kamala] Harris, should they be in office, should understand they will be dealing with Covid for much of their first term,” Jha said. “It will continue to come up as an issue in the next midterms. It’s not going away.”

To put it another way: If Biden takes office, it’s possible a vaccine will finally present some kind of finish line in this pandemic. But we might quickly realize that the finish line is still a few months or years away. And that will make the work of preparing the country for a vaccine — and all the other steps needed to contain Covid-19 in the months and years ahead — necessary. With hundreds of thousands of Americans already dead, it’s the most important task Biden should prepare for right now.

Vice President Mike Pence has not tested positive for SARS-CoV-2, the virus that causes Covid-19. But he’s been in close contact, in recent days, with people with confirmed Covid-19 infections. And he debated Sen. Kamala Harris last night. Was this a good idea?

In a word: No. Per the Centers for Disease Control and Prevention’s own guidelines, Pence should have been quarantining, not debating, even if he’s testing negative. (That said, CDC director Robert Redfield had cleared Pence to debate.)

Since the Trump administration’s actions over the last 11 days have muddied the message from public health experts, let’s be clear: A negative test is not an all-clear for doing risky activities during the pandemic.

Scientists don’t yet understand exactly when a person who is infected with the coronavirus will start testing positive for the virus. There are situations when a person could test negative, actually be infected, and also be contagious. It’s also possible — since this virus multiplies itself exponentially in the body very, very quickly — that someone could test negative in the morning (and not be contagious), but by the afternoon test positive (and be very contagious).

Confusing? Yes, it is. But the bottom line is that Covid-19 diagnostic tests (both the slower, more common, viral genetic test — called RT-PCR— and the more rapid viral protein test, called an antigen test) are most useful, and most accurate, when used on people experiencing symptoms.

“One of the huge gaps now in the data is: What is the probability of testing positive before you get symptoms?” Benny Borremans, a disease ecologist at UCLA, says. Right now, scientists just don’t know for sure.

Why testing is less accurate before symptoms begin

There are several reasons scientists are unsure about when in an infection people will start testing positive for SARS-CoV-2. To understand why, and to make this less confusing, it’s helpful to think through all the things that have to happen for a Covid-19 test to come back positive.

First, the virus needs to take its time to establish itself in a person’s body. This is called the incubation period, and it can take upward of two weeks. On average, this happens in about five or six days. During the incubation period, a person might not test positive for the virus because there’s not enough virus in their body to detect in a test.

“The virus particles, day by day, will multiply,” Muge Cevik, a virologist and physician at the University of St. Andrews, says. “The virus needs to reach a threshold for the PCR [i.e. viral genetic] tests to pick it up.” PCR is the more common Covid-19 diagnostic test because it requires a lower threshold of the virus to test positive; rapid antigen tests would require a higher level of virus to register a positive test.

Testing positive should coincide with being contagious. But not always.

Generally, a person can start being infectious for the virus around two days before they start to show symptoms, in what’s known as the presymptomatic phase.

And, generally — but not always — scientists would expect that if a person is contagious, they’d test positive. After all, if they’re spewing enough virus out to get another person sick, they’re probably spewing enough virus out for a diagnostic test to pick up on.

But there are a few wrinkles here: When exactly a person makes the jump from testing negative and being non-infectious to testing positive and being infectious is hard to predict.

“If everything works as it should, the test should be positive if you are infectious at the very moment of the test, as there must be virus present then,” Justin Lessler, an epidemiologist at Johns Hopkins University, says. “However, you could easily test negative then become infectious a day, or even hours, after the test.” Unless you’re testing every hour, it’s impossible to get a fine-grained view on when the infectious period truly begins. (Also possible, but probably rarer: A person tests positive before they start to be contagious.)

Even if a person is contagious, they may not test positive. It could come down to where the sample for testing was taken from.

In general, “we consider the gold standard to be the nasopharyngeal swab,” Bobbi Pritt, the director of clinical microbiology at the Mayo Clinic, says. “That’s the deep nasal swab that goes all the way back into the back of your nose. Whereas other specimens — like a throat swab or just the very outer edge of your nose, like right inside your nostril — that’s not going to contain as much virus.”

Early on in the infection, a person who is incubating the virus is expected to test negative. Over the summer, Johns Hopkins researchers — including Lessler — published a paper estimating the likelihood of a false negative test in the first few days after being exposed to the virus. On the first day, they found the chance of a false negative is near 100 percent. No test is going to find the virus so early. Through the first four days, that rate drops to 67 percent on day four, on average, but with a very large range of error. On the day people first reported symptoms, there’s still a significant false negative rate, at 38 percent.

What does this all add up to? “What we’re saying is don’t test anyone in less than four days after exposure,” Cevik says. It’s not going to tell you much about the person’s status. Or if a person is tested in that time, they ought to be retested a few days later.

“In general, five to eight days after exposure is the best time to test,” Cevik says. “Or day three after symptom onset.” That’s when the genetic RT-PCR tests are most likely to reveal a true positive.

Because nothing about Covid-19 can be simple, here’s another thing to consider: The antigen tests that produce quick results have a shorter window in which you’d expect a person would test positive.

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They are also slightly less accurate. But if used correctly, they can be very useful: They’ll test positive in the window when a person is most likely to be contagious. With repeated use, scientists hope these quick tests could help stop outbreaks from growing out of control.

The White House, on the other hand, has been using another rapid test, Abbott’s ID Now, to screen asymptomatic people. We just don’t know how good these tests — or any tests, for that matter — are at screening asymptomatic, or presymptomatic, people. “The FDA would be the first ones to tell you that they don’t know how the test is going to perform in that population,” Pritt says.

A negative test without symptoms might not mean much. Keep your mask on.

Here’s the bottom line: “We don’t know when one will test positive pre-symptom onset for PCR or antigen tests,” epidemiologist A. Marm Kilpatrick writes in an email. If you have symptoms, you’re likely to test positive the day you start feeling ill, but not guaranteed. The first few days after starting to feel sick, you have a very high probability of testing positive.

We could learn more in the months ahead about testing asymptomatic and presymptomatic people with studies following people after they have been exposed to the virus, and testing them repeatedly over a few weeks to determine the likelihood of testing positive before symptoms begin. “We have a lot of data from symptom onset onwards, but we don’t have data in terms of pre-symptoms,” Cevik says.

This is why testing is no replacement for other Covid-19 mitigation measures, like quarantining people exposed to the virus, mask-wearing, and social distancing.

“Testing negative is not like a passport for people to go out and do whatever they want to do,” Cevik says. If you might have been exposed to the coronavirus, like Vice President Pence was, you should quarantine for two weeks, regardless of what your test says.

CORRECTION: This post originally misstated A. Marm Kilpatrick’s name. It also mischaracterized Abbott’s ID Now’s test as an antigen test. The test looks for viral RNA.

Kyle Potter, the editor of the travel deals website Thrifty Traveler, is used to flying a lot. But things haven’t been the same since the pandemic. Back in June, when he flew for the first time since Covid-19 hit the United States, it was an eerie experience.

“Pretty much everyone just really feels on edge. I think in a lot of cases, people feel kind of guilty about being on planes right now,” Potter told Recode. “It just kind of all adds up into an unfamiliar experience.”

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The notion of being stuck in a metal tube filled with lots of other people and recycled air seems scary in a pandemic, which is why we’re seeing so many car vacations this year. Plus, many people don’t have the money or motivation to travel long distances. There are those who must travel for whatever reason, and making that experience as tolerable as possible is essential to keep the airlines in business.

Experts estimate it could be years before people fly as often as they did. This bodes very poorly for the flight industry. Months after air travel plummeted at the dawn of the pandemic, money from the government bailout is drying up. That means airlines are now laying off or furloughing tens of thousands of employees, while others are being asked to take pay cuts.

That’s left many airlines and airport-related businesses scrambling for ways to convince travelers that it’s safe — and somewhat easy — to take to the skies. Now some are providing their own Covid-19 testing to travelers, while others are already looking for vaccination-related business opportunities. Overall, these moves hint that more aggressive measures to combat contagion could become a permanent fixture in the future of flying.

Airlines and airports are incorporating Covid-19 testing into travel

In the US, airlines including United, American Airlines, and Hawaiian Airlines are offering options for Covid-19 testing to passengers traveling to the state of Hawaii. These will include at-home tests, drive-through testing, and in-person tests at the airport. With a negative result in hand, travelers will be exempted from the state’s two-week quarantine requirements for new arrivals. American Airlines plans to roll out similar programs for some people traveling to Jamaica and Costa Rica.

Potter expects this trend to continue as international travel slowly resumes. “For all of the countries that are off-limits to Americans — which, to be honest, is most of them — that is going to be … the condition for allowing travel to resume,” he told Recode. “Anywhere you can think of, with very few exceptions, that is going to become the norm, especially for international travel.”

But what about the privacy of people who test positive? Aaron McMillan, United Airlines’ operations policy and support managing director, told Recode that the airline itself wouldn’t keep records of a traveler’s personal health information. But United would get notified from a testing partner “that said customer wouldn’t be able to travel that day” and the airline “would make the necessary arrangements,” he said. Health experts at the airport’s testing site would then provide that United traveler with next steps for receiving care.

For some international travelers, in-airport tests have already become a norm as they travel between different countries. Airports in the US, including Tampa International Airport and Oakland Airport, are beginning to open Covid-19 testing sites of their own, too, and more are set to join.

Even XpresSpa, a firm that normally provides in-terminal spa treatments for travelers, announced this month that, in Newark Airport and JFK, it will offer Covid-19 tests, which cost between $75 and $200 depending on the test or tests you get. Travelers can walk in or make scheduled appointments that take place in the airports’ terminals. The company has also said it’s in conversation with “health passport apps” and looking into creating so-called air bridges between specific cities. The company’s CEO, Doug Satzman, told Recode that, in the future, he even imagines XpresSpa helping with vaccinations for Covid-19 or other illnesses.

The Transportation Security Administration has also made some changes. Instead of a human officer confirming the validity of someone’s identification card, TSA is now piloting a self-service checkpoint using a biometrics-based algorithm designed to confirm that a live photo of a person matches their ID. This builds on the agency’s previous pre-pandemic tests of facial recognition technology, which has also worried privacy experts over potential racial bias, inaccuracy, and surveillance applications.

Then there’s Clear, a company that’s best known for allowing people to bypass TSA screening and head straight toward their carry-on baggage inspection. In the pandemic, Clear has started to offer Health Pass, a biometric-based way of tracking peoples’ health status that was used, notably, to help conduct the National Hockey League playoffs in Canada. (In the NHL case, at least, there have been no recent confirmed Covid-19 cases stemming from the bubble the league created.) Despite the concerns of privacy experts and some members of Congress, Clear has now announced that it will integrate Covid-19 test lab results from LabCorp and Quest into Health Pass.

Clear told Recode that it’s in discussion with airlines and airports about integrating Health Pass into existing security screening processes for the general public. Clear employees are already using the health-based version of the tech at the airport; United, one of the company’s partners, told Recode that it might support Clear’s plans for Covid-19 testing. Amid the pandemic, Clear has taken the opportunity to expand its business model, transitioning from a service that made flying more hassle-free to a business built around confirming peoples’ identities everywhere, as OneZero recently reported.

But the air travel industry having business opportunities with Covid-19 tests reflects the broader failure of the US approach to the public health crisis, argues Kenneth Goodman, director of the Institute for Bioethics at the University of Miami’s Miller School of Medicine.

“The very idea that some people with an extra 200 or 150 — whatever it costs — dollars can buy a test is a sad sign of where our country and where the world is,” Goodman said. “This was not a business opportunity. This was an attempt to try and stop there being too many dead people. And we’ve made a total and complete hash of it.”

Goodman also emphasized that testing negative on a Covid-19 test is by no means an assurance that you haven’t just contracted the illness or that you won’t contract it at the airport or on a plane.

Air travel Covid-19 tests could be a peek at what’s to come

Still, these changes highlight the new normal for air travel anxieties. Potter, of the Thrifty Traveler, says that before the pandemic, fliers were concerned about two primary things: the price of a ticket and in-flight services. Now, many in-flight services are gone, and airlines are most concerned with convincing fliers that it’s safe to be aboard.

The Centers for Disease Control and Prevention, which has issued guidance for air travel, estimated last month that close to 11,000 people were exposed to Covid-19 on flights, according to the Washington Post. As the Mayo Clinic notes, airplanes have sophisticated air filtration systems that can limit the spread of the virus, but a few studies have suggested that Covid-19 can be spread not just on flights themselves but also in security lines and airport terminals.

“To really boil it down, airlines have focused almost entirely on convincing people to get back on planes, convincing them that it’s safe to do so, and trying to get them on and off the plane and through the airport as fast and as safely as possible,” he told Recode.

Airlines and airports have made a point of showing off their cleaning procedures, including litanies of electrostatic sprayers, robot cleaners, and questionable fever-detection tech.

Another move is toward more contactless and biometric technologies. The Australian company Elenium, for instance, has debuted contactless Covid-19 airport kiosks that can hear peoples’ voices and respond to their head movements. These kiosks are now installed in airports in the Middle East, the US, and Australia.

“Even when the Covid crisis dissipates, when there is a vaccine, I think that both the public and business will be sensitive to the impact of future health events, even bad flu seasons,” Elenium CEO Ilya Gutin told Recode in an email. He noted that the company received more leads in the four weeks after announcing its Covid-19-focused kiosk than it had in the past four years.

As airlines begin incorporating Covid-19 testing, they’re also considering what their plans would look like when a vaccine finally becomes available to the public. McMillan, from United Airlines, told Recode that the company was considering how technology might be able to tie information about whether someone was healthy enough to fly to their boarding passes. “We see that evolving into vaccination records,” he said.

“Much like 9/11 changed the security process at the airport, this pandemic will change how people travel with health documentation going forward for sure,” McMillan added, echoing what many airline industry experts told Recode earlier this year.

But Potter is skeptical that people will be flying with the same enthusiasm anytime soon. Even a vaccine, he said, wouldn’t be enough to make flying feel normal again.

“It was really one of the first major industries to feel the pain of this,” he told Recode. “I think it’s probably going to be one of the last to feel the relief, whenever that happens.”

Open Sourced is made possible by Omidyar Network. All Open Sourced content is editorially independent and produced by our journalists.

Researchers at the University of Nevada have reported that a 25-year-old man was reinfected in June with SARS-CoV-2, the virus the causes Covid-19. He joins a handful of other confirmed cases of reinfection in people without immune disorders — in Belgium, the Netherlands, Hong Kong, and Ecuador — where researchers have demonstrated that the genetic signature of the second infection did not match that of the first.

According to a new study on the Nevada case, published in The Lancet Infectious Diseases journal, the patient first tested positive in April, and then tested negative for the virus twice. In June, 48 days later, “the patient was hospitalized and tested positive for a second time,” according to the authors, and he experienced severe symptoms. There were major genetic differences between the two infections, suggesting that the patient got the virus twice. (Since then, the patient has recovered.)

The report is in line with what immunity experts have been telling us is possible with this virus: that reinfection is possible and, to some extent, expected, with a coronavirus. But it also shows us how much we still have to learn: about how much protection a single infection can confer, about what exactly a robust long-duration immune response looks like, and about what determines the severity of disease in a second infection.

“Does immunity protect an individual from disease on reinfection?” writes Yale immunobiology researcher Akiko Iwasaki in an accompanying editorial in The Lancet Infectious Diseases. “The answer is not necessarily, because patients from Nevada and Ecuador had worse disease outcomes at reinfection than at first infection.”

The Nevada case is an important finding, since in the two other confirmed cases of reinfection, the patients had mild disease or were asymptomatic. Scientists still don’t know how common reinfection is (it may well be very rare), nor can they determine an individual’s chances of getting infected again.

They do know there are many, many components of our immune system that work together to fight the coronavirus, and immunity doesn’t mean one single thing. And while we’re waiting for scientists to figure it all out, everyone, including those who’ve already had the virus, should still try to avoid getting infected at all.

The new study “strongly suggests that individuals who have tested positive for SARS-CoV-2 should continue to take serious precautions when it comes to the virus, including social distancing, wearing face masks, and handwashing,” said Mark Pandori, of the Nevada State Public Health Laboratory at the University of Nevada Reno School of Medicine and lead author of the study, in a statement.

Let’s walk through the basics of immunity, and what we’re learning about reinfection.

There are no simple stories about immunity and Covid-19

The immune system is profoundly complicated, and “immunity” can mean many different things. A lot of this nuance gets lost in headlines about immunity.

For instance: Previous research has shown that neutralizing antibodies — immune system proteins that latch onto pathogens and prevent them from infecting cells — can wane in the months after a Covid-19 infection, particularly when the initial infection was mild. Some wondered if that meant the end of herd immunity hopes.

In the Nevada case, we know that “the patient had positive antibodies after the reinfection, but whether he had pre-existing antibody after the first infection is unknown,” writes Iwasaki.

But what’s often misunderstood is that antibodies are only one component of the immune system, and losing them does not leave a person completely vulnerable to the virus.

In fact, there are several parts of the immune system that may contribute to lasting protection against SARS-CoV-2.

One is killer T-cells. “Their names give you a good hint what they do,” Alessandro Sette, an immunologist at the La Jolla Institute for Immunology, told me in July. “They see and destroy and kill infected cells.”

Antibodies, he explained, can clear virus from bodily fluids. “But if the virus gets inside the cell, then it becomes invisible to the antibody.” That’s where killer T-cells come in: They find and destroy these hidden viruses.

While antibodies can prevent an infection, killer T-cells deal with an infection that’s already underway. So they play a huge role in long-term immunity, stopping infections before they have time to get a person very sick.

And it’s not just killer T-cells and antibodies. There are also helper T-cells, which facilitate a robust antibody cell response. “They are required for the antibody response to mature,” Sette says.

Some proportion of the population (perhaps 25 to 50 percent of people) seems to have some preexisting T-cells (of both varieties, but the helper kind have been more commonly observed) that respond to SARS-CoV-2, despite these people never having been exposed to SARS-CoV-2. The hypothesis is that these people may have acquired these T-cells from being infected with other strains in the coronavirus family of viruses. Researchers still don’t really understand what role these preexisting T-cells play in preventing or attenuating infection (if any).

But wait, there’s more! There’s another group of cells called memory B-cells. B-cells are the immune system cells that create antibodies. Certain types of B-cells become memory B-cells. These save the instructions for producing a particular antibody, but they aren’t active. Instead, they hide out — in your spleen, in your lymph nodes, perhaps at the original site of your infection — waiting for a signal to start producing antibodies again.

All the things “immunity” can mean

All these different components of the immune system mean “immunity” isn’t just one thing.

Immunity could mean a strong antibody response, which prevents the virus from establishing itself in cells. But it could also mean a good killer T-cell response, which could potentially stop an infection very quickly: before you feel sick and before you start spreading the virus to others.

“In many infections, the virus does reproduce a little bit, but then the immune response stops this infection in its tracks,” Sette explains. Also possible: “You do get infected, you do get sick, but your immune system does enough of a job curbing the infection, so you don’t get as sick.”

Immunity might also result from an awakening of memory B-cells. If an individual has memory B-cells and is exposed to the virus again, “that infection will stimulate a much faster antibody response to the virus, which would, theoretically lead to faster clearance of the virus and potentially less severe infection,” Elitza Theel, the director of the infectious diseases serology laboratory at the Mayo Clinic, said in a July interview.

In general, scientists believe, the stronger the infection (and immune response) that occurs during an initial infection, the longer immunity will last.

So reinfection may still be possible, but it may not mean severe illness. When a virus invades a body, generally, the body remembers.

Could asymptomatic infections spread the virus? Unclear.

It’s still not known what the latest reinfection study means for how long the pandemic will last. If reinfections happen regularly (and we have no idea how common they might be), then it might take longer to achieve herd immunity without a vaccination (which is an un-ideal, and cynical, goal to begin with). How long immunity lasts, on average, and how common reinfection is are key unknown variables in figuring out how long the pandemic may last in the absence of an effective vaccine or treatment.

“Reinfection cases tell us that we cannot rely on immunity acquired by natural infection to confer herd immunity; not only is this strategy lethal for many but also it is not effective,” Iwasaki wrote in the editorial. “Herd immunity requires safe and effective vaccines and robust vaccination implementation.”

We also have much more to learn about how often reinfections lead to more clusters of cases. Recently, I asked Shane Crotty, an immunologist at the La Jolla Institute for Immunology, about this very scenario.

“Could there be an ‘immunity’ scenario,” I asked, “where, after having recovered from Covid, a person could get infected again but not feel sick at all, and also be able to spread it?”

“It is a good question, and the answer is that no one knows,” Crotty replied. “There are cases with other diseases where asymptomatic immune people can be infectious. There is definitely a lot to learn still about immunity to SARS-CoV-2.”

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Much ink has been spilled over the “replication crisis” in the last decade and a half, including here at Vox. Researchers have discovered, over and over, that lots of findings in fields like psychology, sociology, medicine, and economics don’t hold up when other researchers try to replicate them.

This conversation was fueled in part by John Ioannidis’s 2005 article “Why Most Published Research Findings Are False” and by the controversy around a 2011 paper that used then-standard statistical methods to find that people have precognition. But since then, many researchers have explored the replication crisis from different angles. Why are research findings so often unreliable? Is the problem just that we test for “statistical significance” — the likelihood that similarly strong results could have occurred by chance — in a nuance-free way? Is it that null results (that is, when a study finds no detectable effects) are ignored while positive ones make it into journals?

A recent write-up by Alvaro de Menard, a participant in the Defense Advanced Research Project’s Agency’s (DARPA) replication markets project (more on this below), makes the case for a more depressing view: The processes that lead to unreliable research findings are routine, well understood, predictable, and in principle pretty easy to avoid. And yet, he argues, we’re still not improving the quality and rigor of social science research.

While other researchers I spoke with pushed back on parts of Menard’s pessimistic take, they do agree on something: a decade of talking about the replication crisis hasn’t translated into a scientific process that’s much less vulnerable to it. Bad science is still frequently published, including in top journals — and that needs to change.

Most papers fail to replicate for totally predictable reasons

Let’s take a step back and explain what people mean when they refer to the “replication crisis” in scientific research.

When research papers are published, they describe their methodology, so other researchers can copy it (or vary it) and build on the original research. When another research team tries to conduct a study based on the original to see if they find the same result, that’s an attempted replication. (Often the focus is not just on doing the exact same thing, but approaching the same question with a larger sample and preregistered design.) If they find the same result, that’s a successful replication, and evidence that the original researchers were on to something. But when the attempted replication finds different or no results, that often suggests that the original research finding was spurious.

In an attempt to test just how rigorous scientific research is, some researchers have undertaken the task of replicating research that’s been published in a whole range of fields. And as more and more of those attempted replications have come back, the results have been striking — it is not uncommon to find that many, many published studies cannot be replicated.

One 2015 attempt to reproduce 100 psychology studies was able to replicate only 39 of them. A big international effort in 2018 to reproduce prominent studies found that 14 of the 28 replicated, and an attempt to replicate studies from top journals Nature and Science found that 13 of the 21 results looked at could be reproduced.

The replication crisis has led a few researchers to ask: Is there a way to guess if a paper will replicate? A growing body of research has found that guessing which papers will hold up and which won’t is often just a matter of looking at the same simple, straightforward factors.

A 2019 paper by Adam Altmejd, Anna Dreber, and others identifies some simple factors that are highly predictive: Did the study have a reasonable sample size? Did the researchers squeeze out a result barely below the significance threshold of p = 0.05? (A paper can often claim a “significant” result if this “p” threshold is met, and many use various statistical tricks to push their paper across that line.) Did the study find an effect across the whole study population, or an “interaction effect” (such as an effect only in a smaller segment of the population) that is much less likely to replicate?

Menard argues that the problem is not so complicated. “Predicting replication is easy,” he said. “There’s no need for a deep dive into the statistical methodology or a rigorous examination of the data, no need to scrutinize esoteric theories for subtle errors — these papers have obvious, surface-level problems.”

A 2018 study published in Nature had scientists place bets on which of a pool of social science studies would replicate. They found that the predictions by scientists in this betting market were highly accurate at estimating which papers would replicate.

“These results suggest something systematic about papers that fail to replicate,” study co-author Anna Dreber argued after the study was released.

Additional research has established that you don’t even need to poll experts in a field to guess which of its studies will hold up to scrutiny. A study published in August had participants read psychology papers and predict whether they would replicate. “Laypeople without a professional background in the social sciences are able to predict the replicability of social-science studies with above-chance accuracy,” the study concluded, “on the basis of nothing more than simple verbal study descriptions.”

The laypeople were not as accurate in their predictions as the scientists in the Nature study, but the fact they were still able to predict many failed replications suggests that many of them have flaws that even a layperson can notice.

Bad science can still be published in prestigious journals and be widely cited

Publication of a peer-reviewed paper is not the final step of the scientific process. After a paper is published, other research might cite it — spreading any misconceptions or errors in the original paper. But research has established that scientists have good instincts for whether a paper will replicate or not. So, do scientists avoid citing papers that are unlikely to replicate?

This striking chart from a 2020 study by Yang Yang, Wu Youyou, and Brian Uzzi at Northwestern University illustrates their finding that actually, there is no correlation at all between whether a study will replicate and how often it is cited. “Failed papers circulate through the literature as quickly as replicating papers,” they argue.

Looking at a sample of studies from 2009 to 2017 that have since been subject to attempted replications, the researchers find that studies have about the same number of citations regardless of whether they replicated.

If scientists are pretty good at predicting whether a paper replicates, how can it be the case that they are as likely to cite a bad paper as a good one? Menard theorizes that many scientists don’t thoroughly check — or even read — papers once published, expecting that if they’re peer-reviewed, they’re fine. Bad papers are published by a peer-review process that is not adequate to catch them — and once they’re published, they are not penalized for being bad papers.

The debate over whether we’re making any progress

Here at Vox, we’ve written about how the replication crisis can guide us to do better science. And yet blatantly shoddy work is still being published in peer-reviewed journals despite errors that a layperson can see.

In many cases, journals effectively aren’t held accountable for bad papers — many, like The Lancet, have retained their prestige even after a long string of embarrassing public incidents where they published research that turned out fraudulent or nonsensical. (The Lancet said recently that, after a study on Covid-19 and hydroxychloroquine this spring was retracted after questions were raised about the data source, the journal would change its data-sharing practices.)

Even outright frauds often take a very long time to be repudiated, with some universities and journals dragging their feet and declining to investigate widespread misconduct.

That’s discouraging and infuriating. It suggests that the replication crisis isn’t one specific methodological reevaluation, but a symptom of a scientific system that needs rethinking on many levels. We can’t just teach scientists how to write better papers. We also need to change the fact that those better papers aren’t cited more often than bad papers; that bad papers are almost never retracted even when their errors are visible to lay readers; and that there are no consequences for bad research.

In some ways, the culture of academia actively selects for bad research. Pressure to publish lots of papers favors those who can put them together quickly — and one way to be quick is to be willing to cut corners. “Over time, the most successful people will be those who can best exploit the system,” Paul Smaldino, a cognitive science professor at the University of California Merced, told my colleague Brian Resnick.

So we have a system whose incentives keep pushing bad research even as we understand more about what makes for good research.