How long will COVID-19 last?

The number of new COVID-19 cases in the United States is accelerating, and the impact of the pandemic is “definitely going to get worse before it gets better,” Anthony Fauci, the nation’s leading expert on infectious diseases, said on March 12. “We will have a lot more cases,” Fauci, who directs the National Institute of Allergy and Infectious Diseases, told CNN.

At this point you are probably wondering, am I going to have to self-quarantine forever? Just how long is this pandemic going to last?

Nobody knows what the coming months are going to hold. When asked when life might go back to normal by ABC News on March 15, Fauci stated that it will likely be “several weeks to a few months.” So COVID-19 is going to be with us for a while.

“This is a very clever virus,” says Mark Cameron, an immunologist at Case Western Reserve University in Cleveland. “This is a virus that’s walking around with us, it’s flying with us, it’s going to work with us. And it is of particular concern because of that and the ease that it is spreading between us.”

But we are not powerless. In the United States, how long the crisis lasts will depend heavily on what actions we take now and our ability to gather more information on SARS-CoV-2—the official name for the coronavirus that causes COVID-19 disease—and its spread.

“We are at a pivotal period of time in terms of this unprecedented public health response in containing it and breaking the lines of transmission,” Cameron says. “Could it grow to a point where it takes hold in the population enough to become seasonal? The answer to that appears to be yes. Is it going to strain the health system? Potentially yes, if the very aggressive public health response and measures don’t contain it or are not sustained long enough.”

Here are some of the key questions that scientists are racing to answer that will give us a better sense of how long we’ll be dealing with the COVID-19 pandemic.

When will cases peak?

When an infectious disease first rears its head, there’s an astronomically wide range of possibilities for how it could spread.

“Early in an epidemic the butterfly effect is very real,” says Mac Hyman, a mathematician at Tulane University in New Orleans who worked on forecasts for how the new coronavirus would spread in China. “It matters [if] the first person infected is a bus driver or someone who stays at home.”

In the early stages of an outbreak, individual people’s actions are so unpredictable that researchers can make only short-term predictions based on probabilities—similar to how it’s easier to predict whether it will rain tomorrow than it is to predict the damage hurricanes will cause half a year from now. “After the first few hundred people have been infected then the random effects start to average out and we can predict trends,” Hyman says.

So when might we see a downturn in cases? In a recent paper, British researchers predicted that if no actions were taken to mitigate the spread of COVID-19 in England and Wales, the outbreak in those areas would peak in June, about 4 months after the start of transmission. This work offers a very rough estimate and there are many variables that it couldn’t take into account, says Alex Perkins, an epidemiologist at the University of Notre Dame in Indiana. Still, it does suggest that it will be some time before the new coronavirus calms down in the United States.

“On the order of a few months is probably a reasonable expectation, although that could really change and we’re going to have to update our guesses about that,” Perkins says. Additionally, one grim prediction based on Centers for Disease Control and Prevention scenarios estimates that between 160 million and 214 million people in the United States—which has a population of roughly 330 million—could catch COVID-19 if we don’t act.

However, any outcomes predicted by these models are by no means fated; our forecasts will change depending on what choices we make now and over the next few weeks and months. We’re past the point where we can hope to prevent the virus from traveling far and wide across the country. But we can take aggressive steps to slow its spread. These include personal decisions like washing your hands and working remotely if possible, as well as more sweeping actions.

Already, a number of schools and universities across the nation have closed. Towns in more at-risk areas have enacted curfews, and public gatherings of larger groups have been banned. In New York City, bars and restaurants have closed, Broadway shows are suspended, and the St. Patrick’s Day Parade has been postponed. Meanwhile, Disney World has shut down, the NBA canceled its season after a player tested positive for COVID-19, and many other sports leagues and major events have followed suit.

“All of these things are going to have profound societal effects,” says Sankar Swaminathan, chief of the Division of Infectious Diseases at University of Utah School of Medicine in Salt Lake City. “But I think we’re at that stage. That’s really what I think is going to have to be in varying degrees employed to ultimately bring this under control.”

It will also be challenging to know when we’re actually past the peak of the pandemic, Perkins notes. Even forecasting when the annual flu season will crest is difficult. New cases might drop one week and then rise the next due to chance rather than because of any control measures we’ve taken.

We can draw some insights from other countries that were struck by the virus. Both China and South Korea have begun to report lower numbers of new cases in recent weeks. In China, extensive testing, social distancing, and drastic steps including lockdowns of tens of millions of people seem to have slowed the spread of COVID-19.

“The shortest you could have a really strong effect on decreasing cases is probably about two and a half weeks, but it most likely will be much longer than that,” Swaminathan says. “That’s not to say there wouldn’t still be new cases, but that is probably the most rapid decrement that we could achieve if one were to essentially lock everybody in their houses. Our mitigation steps are going to be not as effective as that.”

Can we slow the rate of new cases?

Based on his research on dengue fever (done mostly in Peru), Perkins has seen a worrying parallel to COVID-19. Those who require hospitalization tend to recover quickly from the disease if they receive proper medical care, he says. But when intense epidemics strike, hospitals become overwhelmed by the surge in new cases and more people die.

We’ve already seen this start to play out with COVID-19 in parts of China and now Italy, where doctors and resources have been stretched thin. Experts are deeply concerned that hospitals in the United States will also become inundated with cases of COVID-19, leading to shortages of supplies and healthcare workers. If that happens, both people with severe cases of COVID-19 and those who need medical attention for other reasons would suffer.

“If everyone got infected today all at once, there’s no way that hospitals could deal with that,” Perkins says.

We want to do everything we can to prevent that kind of spike in cases. That’s why experts have begun to talk about flattening the curve of COVID-19 infections, or spreading new cases out as much as possible over time. Flattening the curve is the goal of the social distancing steps that communities, organizations, and individual people have begun to adopt around the country.

If done properly, these social distancing efforts could make a tremendous difference, Perkins says. “If it’s spread out over time that means that people who do develop more severe forms of the disease and who do need hospitalization will have access to it.”

Because these mitigation steps slow down the appearance of new cases, the outbreak may overall last longer. “But that’s not necessarily a bad thing, because the total number of cases is going to decline,” Swaminathan says. People will still catch COVID-19, but far fewer of those who do become infected will die for lack of doctors or ventilators.

It’s crucial that we take these steps now, even in communities that are not yet reporting large clusters of COVID-19 infections. The longer we wait to act and allow the virus to get a foothold in the community, the longer it will take to bring the rate of new cases down.

“If those measures are successful, and are held in place long enough, the flattening of the curve is more than just spreading out the infection,” Cameron says. “It’s actually breaking the chain of transmission.”

How many people in the U.S. are infected right now?

As of March 17, there are more than 4,500 confirmed cases of COVID-19 in the United States. But the real number is probably much higher. This is partly because many people have mild symptoms and don’t seek treatment. But it’s also because the country has very limited supplies of the test kits needed to diagnose COVID-19.

So far, China has run 320,000 tests in Guangdong province alone and South Korea has screened about 250,000 people and can test around 15,000 people daily. In sharp contrast, the CDC and public health laboratories had only reported testing around 25,000 specimens for the virus as of March 16.

A series of issues—from faulty test kits to initially strict rules about who could be tested and whether private labs would be allowed to develop their own kits—has prevented the United States from testing people on the scale that many other nations have been able to. In a house hearing on March 12, Anthony Fauci acknowledged that the U.S. is not testing nearly enough people. “It is a failing. Let’s admit it,” he said.

Perkins and his colleagues have been analyzing data from the U.S. through early March to very roughly estimate how many infections there actually are in the nation, including both reported cases as well as milder ones that aren’t detected and asymptomatic individuals.

Based on how limited diagnostic testing has been in the United States, he says, it’s pretty likely that we are missing more cases than we are spotting. “It’s difficult to put a precise number on that, but based on the analysis that we’ve done it looks like that number is probably in the tens of thousands,” Perkins says. “And if it’s not already at 100,000 I would guess that it will be probably in a few days or so given how quickly the virus spreads.” Perkins released a preprint of this work on March 16, though the study has yet to be peer-reviewed (the process that scientific results typically undergo before being published). According to the study, even if large-scale mitigation efforts continue, the number of deaths from COVID-19 might not come down for several weeks.

Ramping up our capacity to test people for COVID-19 is a crucial part of finding out how long we might feel the brunt of the pandemic. Widespread testing would tell us how many people are infected, where and when they likely caught the virus, and how widely it’s circulating in the community.

“I think once we have more data about how many people are infected in the community and where in the U.S. there are likely areas where there’s more ongoing transmission…then we could make a more accurate prediction of how rapidly it might spread and what the overall impact might be,” Swaminathan says.

Will the virus slow down in warm weather?

Many respiratory infections—like the flu and common cold—ebb during the summer months. These viruses thrive in cold conditions and spread more easily in the winter, when people are cooped up indoors and closer together. There’s also evidence that some coronaviruses, including the one that causes Middle East respiratory syndrome (MERS), have shorter lifespans on surfaces at high temperatures.

However, scientists don’t know enough about the new coronavirus to predict how warmer weather could affect it, Swaminathan says. And if the virus is vulnerable to toasty conditions, that doesn’t mean it will vanish in summer. Even countries that are currently experiencing hot weather such as Australia and Brazil are seeing cases of COVID-19.

“This is a novel coronavirus—none of us has immunity to it, so it’s not going to completely go down to nothing no matter how warm it gets most likely,” Swaminathan says. “There will be low-level circulation, which will then potentially come back with a dramatic resurgence in the winter.” This has happened before during pandemics in populations with limited preexisting immunity, such as the Spanish flu pandemic of 1918.

Climate may play a role in the spread of the new coronavirus, meaning it could spike in the autumn and winter and fall in the spring and summer, Perkins says. But this effect would be more likely to kick in several years from now if the virus becomes endemic in our population and becomes a seasonally recurring problem.

“In the context of this pandemic when everyone is susceptible, or started out susceptible, and it’s just spreading like crazy, I don’t think we can count on the weather to get us out of this situation,” Perkins says. “We really have to approach this situation now as if the weather is not a factor.”

Still, there are advantages to figuring out how temperature-sensitive the new coronavirus is. On March 9, scientists published a very preliminary report suggesting that the virus may transmit more easily in relatively cool conditions. The researchers found that the regions that have been hit hardest have similar winter climates with average temperatures between 41 to 52 degrees Fahrenheit and average humidity levels ranging from 47 to 79 percent. And the areas that first saw community spread of the virus—including China’s Hubei province, where the virus first appeared; northern Italy; parts of Iran, Japan, and South Korea; and the Pacific Northwest in the United States—were located within a narrow band of latitudes.

“There are many factors that go into how and why an outbreak occurs at a certain location,” Mohammad Sajadi, an associate professor of medicine at the University of Maryland School of Medicine’s Institute of Human Virology in Baltimore and coauthor of the new research, told Popular Science in an email. However, he and his colleagues predict that as temperatures rise in early spring, areas experiencing temperate conditions now or in the near future will face a heightened risk of large outbreaks. “We’re already seeing that in the Northeast and Northwest,” he said.

The work has not yet been vetted by other researchers, and more evidence will be needed before we can draw any firm conclusions about how the new coronavirus is impacted by weather patterns.

“We don’t want people to think the problem will magically disappear with warmer weather,” Sajadi said. However, if the new findings are corroborated, he said, we might be able to predict when different parts of the country will be most vulnerable to COVID-19.

What can we learn from other outbreaks?

We can take lessons from other coronavirus outbreaks and historic pandemics.

Part of the reason that the SARS epidemic—which was caused by a different kind of coronavirus—was tamped down so quickly was that the virus made almost everyone who caught it very sick. This made it easy to trace the spread of the virus. The new coronavirus, on the other hand, causes relatively mild symptoms in most people, and sometimes none at all. This means it has more opportunities to spread unnoticed through the population.

In the city of Toronto, SARS cases began appearing in the winter of 2003 and then calmed down towards the end of spring. This wasn’t because summer was coming, though, says Cameron, who was part of the Canadian SARS Research Network that responded to the outbreak. “What stopped the SARS virus was a very efficient public health response,” he says. “The question for me, is how long do we keep these measures in place knowing their impact on the economy and the community?”

The city of Toronto saw two waves of SARS cases because it relaxed its emergency guidelines too soon. “They felt that they had broken the chain of transmission, but they hadn’t,” Cameron says.

Despite their connections to nations in the grip of severe COVID-19 outbreaks, reports of new cases have been relatively low in Singapore, Hong Kong, and Taiwan. All three of these places were struck by SARS nearly two decades ago, and they did not forget the danger posed by new viruses. Instead, they began planning for future outbreaks.

It’s too soon to know how effective the responses in these locations will ultimately be. But their surveillance, mitigation, and public health education measures do seem to have slowed their COVID-19 outbreaks for now while still being less draconian than the lockdown that China had to implement.

South Korea also adapted its disease-response strategies after an outbreak of MERS in 2015, which has allowed it to implement the widespread testing that has helped reign in the coronavirus for now.

Among many other pressing questions we can’t yet answer are whether the virus spreads through feces and what role children—who tend not to become very ill when they’re infected—play in transmitting COVID-19. “We just don’t know what will happen with this virus in the long-term,” Sajadi said. “There is still much we don’t understand about it.”

But history shows us how much of a difference social distancing can make. During the Spanish flu pandemic, the city of Philadelphia ignored warnings that the disease was spreading in the community and threw a war bond parade—and within the week thousands of people died. St. Louis, on the other hand, reacted quickly when its officials detected cases of the flu. The city closed schools, libraries, churches; banned public gatherings of more than 20 people; staggered work shifts; and more. The upshot: far fewer people died in St. Louis than in Philadelphia.

Scientists can also build on work that began with the SARS epidemic on vaccine or antiviral treatments for the new coronavirus.

“Even though some of the work stopped and some of the funding stopped, a lot of the scientific community kept working on coronaviruses in anticipation of something exactly like this,” Cameron says. “So the research for therapy or vaccines for SARS-CoV-2 or treatments for patients with COVID-19 illness did not start from scratch.”

How do our immune systems respond to the coronavirus?

Since this particular coronavirus has never been seen in people before, none of us has immunity from past infections.

“One of the factors [that will] determine what the peak and decline eventually looks like will be whether infected persons develop long term immunity,” Colm Atkins, a virologist at Rutgers University–New Brunswick in Piscataway, said in an email. “In some cases this happens, and we can exploit that characteristic to make vaccines like measles and mumps, but in other cases, such as noroviruses, infected people do not appear to develop robust immunity.”

It’s not clear yet if people can catch COVID-19 twice. There have been reports of people recovering from COVID-19 and then testing positive again later. However, the most likely explanations are errors in testing or that these people had a relapse of their symptoms or were released too soon, experts say. Anthony Fauci has also stated that it’s unlikely that you can become re-infected with COVID-19.

As more and more people recover from COVID-19, we’ll begin to see herd immunity develop in the population and blunt the virus’s spread. However, it’s really hard to eliminate a disease once it becomes entrenched, Perkins says. Smallpox (caused by the variola virus) is the only infectious disease that we’ve completely eradicated off the face of the planet.

“In terms of how long it lasts, I think it really is a combination of population immunity and how quickly that develops…but also what steps people are taking to prevent themselves from getting infected and how long those behaviors and other adjustments are in place,” Perkins says. “But realistically, I don’t think it’s ever going to go away completely. I think there’s going to be a continual risk of this for a long time.”

Scientists are working at breakneck speed on a vaccine for COVID-19, but it won’t be ready for at least a year to a year and a half.

“In this first year of the epidemic vaccines are pretty much out of the question; in the future they will be probably one of our major defenses,” Hyman says. “But for right now what we really need to do is to find ways to keep people alive once they’ve been infected.”

So, how long will it last?

According to Jennifer Horney, the founding director of the University of Delaware’s epidemiology program in Newark, the less effective community and individual measures are, the longer our country will continue to see new cases. “For the next few months I believe we can expect increasing case counts as testing becomes more widely available in the U.S., and the virus continues to expand its reach globally,” she told Popular Science in an email.

The overall outlook for the pandemic will become clearer a few weeks from now,

Swaminathan says. He likens our present situation to forecasting the track a hurricane will take. As the storm approaches the shore, the “cone of uncertainty” that meteorologists use to represent its possible path narrows.

The social distancing steps that people in the U.S. have started taking over the past week are heartening, Cameron says. “But I don’t know the answer to how long those measures have to stay in place,” he says. “We cannot become complacent in protecting the most vulnerable members of the community that will be more severely hit by this virus, even if in general the majority of cases are mild.”

If we do see reports of new cases begin to fall and let down our guard too soon, the virus could come back with a vengeance—which is still a risk in China. However, a timeline for social distancing will have to balance the need to minimize surges in new cases of COVID-19 with the fact that the social and financial safety net does not exist for millions of Americans, Atkins said.

“Social distancing or no, children who get food at school will have to be fed, stadium workers not working at MLB games will have to be able to pay rent, and medical care needs to be available and affordable to everyone,” he said. “Even if one person is able to isolate, we depend on the labor of those who cannot afford to do so.”

When it comes to predicting how long the most intense period of the coronavirus pandemic will last, there are no easy answers. But one thing is clear: the sooner we shut down large gatherings and those of us who are able stay home actually do so, the less time we will have to wait before the virus slows down.

“The best tool right now is this aggressive public health response and tracking the virus where it is and who has it,” Cameron says. “The other side of that equation is making sure that research is funded, and funded consistently, so that we can either deal with this particular virus if it comes back or another coronavirus that may take its place.”