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Medical workers in White Plains, New York, on April 29.
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11 questions about the coronavirus we still can’t answer

Here’s what we don’t know about the coronavirus — and why it really matters.

When speaking to experts about the coronavirus pandemic, there’s one answer I’ve had to get very comfortable with: “I don’t know.”

There are some things we know about the coronavirus and the disease it causes, Covid-19. It’s dangerous — much deadlier than the seasonal flu. The countries that have managed to control their outbreaks largely did so with a mix of social distancing, widespread testing, and contact tracing. It generally hits older people harder, although the young can still be vulnerable, even if they’re healthy.

Scientists are also making new discoveries about Covid-19 every day: It appears to sometimes cause strokes in the relatively young. It may have mutated. It’s probably slowed by warmer, sunnier weather, but almost certainly not by enough for summer to save us.

But there is a lot we don’t know. Although it can often feel like we’re an eternity into this disease outbreak, the reality is the SARS-CoV-2 virus that’s warped all our lives is still very new to humans and there is still a lot that we have to learn about it.

I spoke with a dozen experts about what we don’t know about the coronavirus. They presented all sorts of questions we still don’t have solid answers to: How many people have been infected? Why have some places avoided big coronavirus outbreaks so far? What forms of social distancing work best? Do we develop lasting immunity to the virus? Can we really get a vaccine within 12 to 18 months?

“It’s the hard part for a lot of people; they think we should have very concrete answers,” Saskia Popescu, an infectious disease epidemiologist, told me. “But, realistically, we’re building a bridge as we walk across it. This is a novel disease. This is a novel situation. And it’s harmful to make rash decisions not based on any data or science.”

The answers could decide, for example, just how deadly this coronavirus is. They could show if the US, states, and cities are safe to reopen parks and beaches — or even schools. They could help us prepare for the possibility that the coronavirus will become endemic, meaning it could come back regularly, or if a vaccine or similar medical treatment will offer us a way out in a year or more.

That’s also what can make these questions so uncomfortable. The stakes are high, with hundreds of thousands or even millions of lives at risk in the US alone. That uncertainty adds to the fear and frustration we’re all already dealing with.

But experts say it’s important to deal with that uncertainty responsibly. We need to be cautious, particularly of answers that we want to hear even if there’s not much evidence for them. We need to be ready to adapt, especially when this virus goes against expectations. We need to be ready to confront the possibility some things are even worse than we hoped — but maybe at least other things will turn out better than we feared.

In that context, here are 11 major questions that experts still have about the coronavirus — and the implications of the answers, whatever they may be.

1) How many people have been infected?

We know that, as of May 11, there are nearly 4.2 million confirmed or presumed coronavirus cases around the world; more than 1.3 million of those are in the US. Almost 285,000 deaths have been linked to the virus globally, and nearly 80,000 deaths have been linked to it in the US.

But every expert I’ve spoken with has agreed on one thing: These are undercounts. There aren’t enough tests, tracing, or overall surveillance to track every single infection in such a widespread disease outbreak. Even people who get very sick or die sometimes do so in the privacy of their homes. There are potentially millions of Covid-19 cases around the world that we’re missing, and tens of thousands or even hundreds of thousands of missed deaths.

There’s a good chance that we’ll never really know the exact answer to this question; after all, there is still some scholarly debate about how many people were infected and died during the 1918 flu pandemic.

A more precise answer to this question has important implications: If it turns out way more people are infected but not many more are dying, then maybe the coronavirus isn’t as deadly as we thought. At the very least, if more people have been infected than we thought and are now immune (still a very big if), then maybe lockdowns could end earlier. If it turns out we aren’t missing many infections or we are proportionally missing as many deaths as infections, then continued vigilance is warranted.

“Fundamentally, knowing your rate of hospitalization and the true burden of infection would really influence the way that we rightsize the response to this outbreak in whatever location you’re talking about,” Amesh Adalja, a senior scholar at the Johns Hopkins Center for Health Security, told me.

The question of how many people are infected is particularly complicated because we know there are some people who spread the virus or test positive without showing any symptoms. That raises the possibility that there are a lot of people who’ve been infected without knowing it.

But we don’t know if those people remain asymptomatic. A preliminary study that followed an outbreak at a South Korean call center found most of the infected developed symptoms early on or within 14 days of quarantine. If that holds up in more research, it indicates we might not be missing as many cases — suggesting that we won’t get a break on the overall death rate.

“We need to know how transmissible this is,” Tara Smith, an epidemiologist at Kent State University, told me. “We just don’t know that.”

Besides masking the extent of the pandemic, widespread asymptomatic or presymptomatic transmission could also necessitate blunter forms of social distancing since it means that someone staying home if they have symptoms may not be enough. And it boosts the need for mask-wearing since people wearing masks are less likely to spread the virus.

As researchers dig up some answers, the experts I spoke with urged caution. We’ve seen horrible outbreaks across the globe — in Italy, Spain, and New York, for example — so we know that the coronavirus can be very dangerous. This is really about finding out just how dangerous it is, not whether it’s fine to ignore the pandemic and carelessly go on with our lives.

2) Can the US really scale up coronavirus testing and tracing?

When I asked experts in March what the US needs to do to confront the coronavirus, I got the exact same answers I got in April and am now getting May: scale up testing and tracing. With that, the US could track the full outbreak, isolate the sick, quarantine their contacts, and deploy community-wide efforts, including lockdowns or extreme social distancing, as necessary.

Without testing and tracing, the US is flying blind — and Americans are more likely to stay stuck at home. Some countries, such as South Korea and Germany, have managed to get their outbreaks under control and ease some social distancing measures. But they did that by setting up rigorous testing and tracing measures that let them put out embers before they become wildfires.

There have been some positive developments in the US. Based on the COVID Tracking Project, the number of tests averaged about 276,000 the week of May 3 — up from about 150,000 in early April. The positivity rate, which measures what percent of tests come back positive for Covid-19, has fallen below 10 percent nationwide and in most states, which experts say is one important benchmark for adequate testing.

A chart showing the number of coronavirus tests in the US each day. German Lopez/Vox

Still, the number of tests falls far short of the 500,000 to tens of millions of tests experts argue is necessary. America’s positive rate of 9 percent is also much higher than that of better-faring nations, including South Korea. The US still needs to pair testing with 100,000-plus contact tracers, who would work to isolate and quarantine the sick and their contacts.

There’s no question about whether testing and tracing are necessary. The question is whether the US can take the steps necessary to overcome the bottlenecks, including supply shortages for swabs, reagents, and other materials needed. This will require serious federal leadership. So far, President Donald Trump’s testing “blueprint” explicitly leaves the problem to the states and private sector, saying the federal government will only act as a “supplier of last resort.”

Some experts argue this is a massive failure of America’s political system. “This is a disease that does not just test your health system,” Jeremy Konyndyk, an expert in disease outbreak preparedness at the Center for Global Development, told me. “It tests your political system. It tests the quality and competence of your governance.”

It’s unclear if Trump or other federal leaders will straighten up and if these problems will be resolved in time. If not, maybe state governors will band together and fix the problems, or the private sector could develop a reliable, accessible at-home test that more people can get. But right now, there’s still uncertainty over whether the country will get its act together.

3) What forms of social distancing work best?

When employers, cities, states, and countries closed down in response to the coronavirus, many did so bluntly — shutting down just about everything that could be shut down.

With so little known about Covid-19 and how the virus spreads, a lot of places figured it’d be better to be safe than sorry. So they closed down whatever they could.

For researchers, that creates a problem, because it makes it hard to tease out which forms of social distancing are to credit for the slowdown of any spread. Bans on large gatherings? Restrictions on air travel? People working from home instead of an office? Something else?

People maintain social distancing outside a pizzeria in Brooklyn while waiting for their takeout orders on May 10.
Erik McGregor/LightRocket via Getty Images

The largest risk seems to come from places “where people are in close proximity indoors for extended periods of time,” Natalie Dean, a biostatistics professor at the University of Florida, told me. Beyond that, there’s still a lot of uncertainty. Why, for example, have there been big outbreaks in meatpacking facilities, compared to other kinds of “essential” workplaces?

Some researchers are working on those questions, applying what we already know about the coronavirus and the experiences of places that followed different paths to see what wins out in a cost-benefit analysis. South Korea and Germany, for instance, are taking careful approaches to reopening that will help evaluate what seems to increase the risk of spread the most. Second waves in other places, such as Hong Kong and Taiwan, could also help demonstrate what doesn’t work.

The implications are crucial to getting our lives back to normal and getting the economy back on track. They could help dictate what the right cut-off for gathering restrictions is — 10 people, 20 people, 50 people, or something else entirely. They could help decide if restaurants can open up at 10, 20, 50, or 100 percent capacity. Perhaps a quick bus trip is fine even if a long plane ride isn’t. Maybe some places, like schools or parks, don’t have to remain closed, or it might be okay to visit friends and family in outdoor areas.

Even if the answer is that we need to lock down as much as possible, what’s possible still remains an open question — not just in terms of what people will tolerate but what they can tolerate.

“If you lock people in their house for two to three years, how will they work to get food? How will we produce things people need to live? How will other medical conditions fare?” Adalja, of Johns Hopkins, said. “There is a balance. … The solution can’t be to basically end industrial civilization until there’s a vaccine, because the very vaccine you need is based on industrial civilization.”

4) Can children widely spread the coronavirus?

Months into the pandemic, we still don’t really know what role children play. “It’s the most important question to my mind,” Bill Hanage, an epidemiologist at Harvard, told me. “It’s still not clear.”

At first, it wasn’t clear that children could even get sick and transmit the virus. With more time, we’ve learned that, unfortunately, kids can get sick — with recent reports appearing of coronavirus-positive children developing mysterious symptoms, such as enlarged coronary arteries. They don’t seem to get nearly as sick as older groups, but it doesn’t seem they’re totally safe, either.

A senior walks with a child riding a bike near the Brooklyn Bridge in New York on April 27.
Michael Nagle/Xinhua News Agency via Getty Images

What we know less about is just how much kids spread the virus. Some research is ongoing, but experts say it’s far from conclusive.

Beyond how the virus works in kids, human behavior can complicate potential answers, Hanage said. “Even if kids transmit less per contact, maybe kids make many more contacts or are less able to do social distancing. So the net effect is that they still contribute more to the pandemic.”

This could help decide if, for example, schools need to close down. Many places shut down their schools under the assumption that kids could be vectors for Covid-19, as they are with the flu.

But maybe — hopefully — kids aren’t big transmitters. If so, schools could reopen safely. That would have important implications not just for their education but also on the many aspects of modern life that rely on schools to function, like parents who need a break from parenting to work (or for their sanity) and kids who rely on school lunches.

If it turns out that kids do transmit the virus to some degree (as some experts say is likely), findings showing that they transmit the virus less than adults could still let schools reopen at reduced capacity. Maybe classroom sizes will be smaller, desks will need to be spread out, and cafeteria hours will be more phased apart. Even that, though, would be a welcome break for many parents — and a prerequisite to reopening parts of the economy.

5) Why have some places avoided big coronavirus outbreaks?

One of the most persistent questions throughout the pandemic has taken this form: Why did New York suffer a bigger outbreak than California? Why is Michigan doing much worse than Ohio? Most recently, I have become obsessed with another comparison: Why is Tokyo doing so much better than New York City, even though Tokyo is denser, makes more use of public transportation, and even has similar weather — all factors that likely contribute to the virus’s spread?

In some cases, the answers are comforting: The places that acted quicker and much more aggressively seemed to do better. That means we do have some control over this disease.

A sign reminds the public of social distancing rules along the Third Street Promenade shopping street in Santa Monica, California, on May 8.
Frederic J. Brown/AFP via Getty Images

But often, the answers aren’t so comforting. Luck can be a huge factor; sometimes, all it can take is a single superspreading event, in which one person or a few people spread the disease widely, for an outbreak to get out of control. A population’s age and health can also determine if Covid-19 is extremely deadly. Broader societal factors, like population density or the use of public transportation, can further the spread of the coronavirus.

And sometimes there really aren’t any clear answers. Look at New York City versus Tokyo: With higher population density and greater public transportation use, Tokyo should, at least in theory, be doing worse. Tokyo and Japan’s leaders were slower to take action against the virus than their New York and US counterparts. Testing rates in Japan remain abysmal — as of May 7, its daily testing rate was nearly one-twentieth of America’s.

But the reality is there are simply a lot of differences, known and unknown, between New York City and Tokyo that researchers will have to tease out in the years ahead to figure out why Japan’s most populous city seemed to fare so much better than America’s. Maybe it’ll turn out that masks, which Japan widely adopted years ago, play a bigger role in stopping transmission than initially believed. Maybe Tokyo follows better hygiene practices. Maybe Tokyo’s population is healthier than America’s, even if it’s older. Maybe Tokyo just got lucky (at least so far). Maybe there’s a significant variable we’re all missing.

“I don’t know what explains it,” Hanage said. “Please make clear that we’re talking speculation here.”

There will surely be a ton of this line of questioning — and scientific inquiries — in the years to come. “We can get some preliminary, superficial understanding of it, but it’s going to take a while for us to really understand that,” Popescu, the infectious disease epidemiologist, said.

When those answers do come, though, they’ll help guide how cities, states, and countries respond to Covid-19 outbreaks as well as other respiratory illnesses and infectious diseases in the future.

6) What effect will the weather have?

We do know that summer alone isn’t enough to save us from Covid-19. If warm, sunny, and humid weather was enough, there simply wouldn’t be big outbreaks in Louisiana, Ecuador, and Singapore, all of which regularly report temperatures above 80 degrees Fahrenheit and humidity above 60 percent.

But the research does indicate that heat, humidity, and UV light all seem to hurt the virus. Higher temperatures can help weaken the coronavirus’s outer lipid layer, similar to how fat melts in greater heat. Humidity in the air can effectively catch virus-containing droplets that people breathe out, causing these droplets to fall to the ground instead of reaching another human host — making humidity a shield against infection. UV light, which there’s a lot more of during sunny summer days, is a well-known disinfectant that effectively fries cells and viruses.

“There are multiple coronaviruses out there that affect our population, and many of them, if not most of them, exhibit a seasonal influence,” Mauricio Santillana, the director of the Machine Intelligence Lab at Boston Children’s Hospital and a researcher on the effects of the weather on the coronavirus, told me. “The hypothesis postulated for Covid-19 is that it will have a similar behavior.”

It’s a hypothesis that researchers are still testing, both in labs in which they throw heat, humidity, and UV light at the virus as well as real-world experiments and models in which they see how the virus is faring in warmer, more humid, and sunnier conditions. So far, the evidence suggests the weather has some effect — but not enough to stop the spread of the virus on its own.

A big complication is that, unlike other coronaviruses and the flu, most people don’t have much, if any, immunity against the Covid-19 virus. “While we see some influence [of the weather], the effect that we’re seeing — if there’s any effect — is eclipsed by the high levels of susceptibility in the population,” Santillana said. “Most people are still highly susceptible. So even if temperature or humidity could play a role, there’s not enough immunity.”

Maybe once we do build up that immunity, weather will play a more important role. That could be particularly important if the coronavirus becomes endemic since it could limit how much it appears in the summer compared to the spring, fall, or winter. It could also mean that, if the pandemic rages on in the months and potentially years ahead, summer could let us relax some social distancing measures that would be required otherwise.

Again, the lessons of Louisiana, Ecuador, and Singapore suggest we can’t fully reopen as soon as the summer weather hits. But depending on where the research lands, there’s some hope for the future.

7) Can we reopen parks and beaches?

One implication of the research on warmer weather is it could be safe to reopen parks, beaches, and other outdoor spaces. It’s already widely accepted that open-air areas are much less likely to be vectors of the virus spreading — the virus spreads through droplets, and those droplets are simply less likely to reach another person in well-ventilated places. But if heat, humidity, and UV light help as well, then maybe it’s even safer to go outside for a bit.

“Biologically, it makes sense,” Dean, of the University of Florida, said. Spending time outside “is good for people, too.”

People relax at Echo Park Lake in Los Angeles, California, on May 10.
Michael Tullberg/Getty Images

As social distancing drags on, the possibility of going to the park or beach offers a welcome reprieve to staying home all day. As we see signs that people are already getting fed up with extreme levels of social distancing, the break that beaches and parks offer may be a needed form of harm reduction — making the other forms of social distancing that are still needed a bit more bearable.

Some experts have already concluded that reopening these outdoor environments is fine. But there are still some questions about how to do it: What kind of physical distance should people keep from each other? Is it okay if people meet with friends or family they don’t live with at parks or beaches? Is it a bad idea for people who are more vulnerable to Covid-19 — those who are older or have comorbidities — to go to the park or beach?

For now, the experts I spoke with suggested that people in outdoor public areas remain six feet away from each other, wear masks, and avoid large gatherings. But depending on what researchers find, it could turn out that we’re being too cautious — and, at the very least, it might be okay to reopen up such spaces more broadly, though likely with some restrictions.

8) Do we develop lasting immunity to the coronavirus?

Here’s a scary but real possibility: Even after you get sick with Covid-19, you might not develop immunity to the virus for long. It’s possible that immunity could only last weeks, months, or years. We just don’t know yet.

This isn’t unheard of with other diseases. Most of us have dealt with multiple colds and flus in our lives. Some people don’t develop immunity to pathogens in the same way as others. As Brian Resnick and Umair Irfan explained for Vox, the immune system is very complicated and frequently defies expectations.

With the coronavirus, there have been reports of reinfections. But it’s not clear if those are actual reinfections, if the detected reinfections are actually a result of false negatives or false positives in testing, or if something else is going on.

Senior Airman Serena Nicholas administers a coronavirus test to a first responder in Chicago, Illinois, on March 26.
Brian Cassella/Chicago Tribune/Tribune News Service via Getty Images

If immunity to the coronavirus is temporary, there’s a chance that outbreaks of the virus could pop up again and again in the future. That means this could be the beginning of a new endemic disease, coming back regularly in new waves and possibly even new strains. Even if we develop a vaccine, it might offer only temporary protection.

That doesn’t mean the next outbreak will be as bad as it is right now. With the flu, we’ve developed vaccines and other treatments that have generally made it less dangerous. It’s also possible that past infections will build up some protection in the body even if it’s not full immunity.

And there’s a possibility that we do develop full, lasting immunity. Or maybe the virus will somehow die out otherwise, as happened with SARS (although that seems unlikely, given that Covid-19 is already so widespread).

For now, though, preparing for the worst means preparing for the possibility that this is only the first of many coronavirus outbreaks.

9) Can the world really push out a vaccine in 12 to 18 months?

It’s become a common refrain in media reports that a Covid-19 vaccine is potentially 12 to 18 months away.

But as Stuart Thompson explained in the New York Times, this would be unprecedented. The previous record for developing a vaccine is four years. The actual timeline for a Covid-19 vaccine could span anywhere from six months — at the most hopeful end — to 16 years.

“It seems very optimistic to think we could have a vaccine this fall or even in the next year,” Josh Michaud, associate director for global health policy at the Kaiser Family Foundation, told me.

There are ways to speed up the process. Bill Gates, for one, has promised to build vaccine factories to speed up the manufacturing process. Human challenge trials, in which healthy people are directly exposed to the virus, could help test for immunity more quickly.

But in vaccine development, time can be an important, unavoidable factor. Researchers need months to see if a vaccine actually provides protection for months and if it leads to dangerous side effects months down the line. They need time to see how a vaccine that works in a lab setting interacts with the real world.

There’s another grim possibility: “We may actually not ever get a vaccine for Covid,” Zoë McLaren, a health policy expert at the University of Maryland in Baltimore County, told me. As she explained it, vaccines are a high-risk, high-reward investment, one that inherently carries the possibility that an effective, safe vaccine never pans out.

The upshot is that if we rely on a vaccine to reopen the economy, we could be doing some level of social distancing in the months and years ahead. That uncertainty should lead us to pursue other avenues for reopening, such as widespread testing and tracing.

Even if we can develop a vaccine, there’s a risk of rushing it. In 1976, America rushed out a vaccine in response to fears of a widespread swine flu outbreak. It turned out the swine flu that year wasn’t as widespread as officials feared, and the improperly tested vaccine led to a rare neurological disorder, Guillain-Barré syndrome, in 450 people. “It caused more harm than it saved,” Michaud said.

Vaccine production has come a long way since 1976. But it’s come a long way in part because we have regulations and safeguards to try to guarantee efficacy and safety, and those protections might slow the arrival of a cure beyond the 12- to 18-month window.

Still, some people remain hopeful. “I’m optimistic,” Dean, of the University of Florida, said. “There’s just so much work being done in parallel.”

10) Will we get other medical treatments for Covid-19?

Even if we never get a coronavirus vaccine, there’s another possibility for a break: We could find other treatments that may not cure Covid-19 but make it much less dangerous.

This isn’t unprecedented. We have never developed a safe, effective HIV vaccine. But we have developed antiretrovirals that can combat HIV so well that it becomes undetectable in the body — even preventing its spread — and other treatments that make it much less likely someone will catch the virus from someone who’s HIV-positive. There are many differences between HIV and the coronavirus, but this shows that there are alternatives to a vaccine.

With the coronavirus, research into non-vaccine treatments is still fairly early. So far, the results have been mixed with remdesivir and disappointing with hydroxychloroquine. But it’s early, so there could be a big breakthrough at some point.

Better treatment could also come down to better medical processes. For example, we’re still learning what comorbidities put people at greatest risk; it seems like obesity, heart disease, and diabetes, among other conditions, could put people at greater risk of contracting the coronavirus. We’re also still learning about what kinds of symptoms and complications the virus leads to, as we’ve seen in recent reports about strokes potentially linked to Covid-19.

“We need more refined answers,” Adalja, of Johns Hopkins, said. For example: “Is it really the obesity, or is it because most of those people are diabetic? How does that all interact with each other?” The answers, he added, could help dictate the health care needs of such patients.

As medical professionals and officials figure all this out, they’ll be able to better prioritize and treat patients with Covid-19. As long as they have the capacity to treat the disease — still a work in progress — that could significantly decrease the risk of serious complications and death. It could also help narrow down who needs to follow stricter social distancing — maybe some healthy people with no family history of certain health conditions could be out and working more.

11) Do we need all these ventilators?

Early on in the crisis, it was widely assumed that the US would need a lot more ventilators than it currently has to help patients who develop breathing problems as a result of Covid-19.

That turned out to not be the case. For one, social distancing seemed to slow the spread of the virus enough that even places that have been hardest hit, like New York, have been able to cope without some of the surge capacity they secured.

But there’s also some evidence that ventilators may not be as helpful as once believed. It seems overuse of ventilators is actually possible with Covid-19, meaning some patients may actually be harmed if they’re on ventilators too long. Doctors also developed ways to treat patients that reduce the need for ventilators. And, unfortunately, some evidence now suggests that ventilators may not help as much as hoped.

“We need more time,” Popescu, the infectious disease epidemiologist, said. “It’s going to be a while until we really understand some of the medical interventions that work and don’t work.”

There’s a dark side to this story here: It turns out a treatment that we hoped would help people with Covid-19 may not be as successful. But there’s a promising development, too: Maybe we don’t need as much of these somewhat complicated machines to stop the worst.

All of this comes with a big caveat: We are still early in our understanding of Covid-19, so it could turn out that our understanding of ventilators and their use changes more over time.

Really, that’s the caveat with so much about the coronavirus. At the end of the day, we’re still learning so much about this pathogen and how it’s going to affect the rest of our lives.

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