How will we know whether the coronavirus will come back stronger in the winter?

Dr. Robert Redfield speaks at the White House
Dr. Robert Redfield, director of the Centers for Disease Control and Prevention, has warned that the coronavirus could enjoy a resurgence come winter.
(Alex Brandon / Associated Press)

Even as policymakers discuss potentially reopening state and local economies, state and federal officials are warning of the need to be prepared for a potential “second wave” of the coronavirus outbreak once the initial one dies down.

But is a second wave inevitable? The answer depends on the nature of the virus itself, our own behavior and the degree to which we prepare for another surge, experts said.

While scientists are still trying to understand the ins and outs of the virus that has infected more than 2.6 million people around the world and caused more than 186,000 COVID-19 deaths, they can make some educated guesses about how long it will remain a menace by studying the behavior of other coronaviruses.


There are actually several types that can infect humans, including four that are responsible for about a quarter of our common colds. Though the new SARS-CoV-2 variety is more dangerous, the fact that it’s a coronavirus suggests it may have characteristics in common with its older cousins.

The cold-causing viruses are in fact pretty seasonal — the number of people they sicken spikes in the winter and spring, then transmission declines during the summer, said Dr. Amesh Adalja, an infectious disease specialist at Johns Hopkins University. There’s no reason, at least biologically, to think that SARS-CoV-2 would buck that seasonal pattern.

“I suspect this will come back [and] if we do get any kind of lull in the summer that this will likely pick up in the fall, just like other coronaviruses do,” Adalja said.

One reason for those summer lulls is that coronaviruses are not all that hardy in the environment, he said. Generally speaking, they don’t do well in hotter, more humid, sunnier weather, in part because they’re vulnerable to ultraviolet light and wrapped in a lipid envelope that can dry out as the temperature climbs.

That doesn’t necessarily mean COVID-19 cases will peter out to the same extent as coronavirus-induced colds, he added, since immunity would be more of a factor for viruses that have been in circulation for a long time. SARS-CoV-2 is so new that this kind of buffer doesn’t really exist — at least, not yet.

When summer comes, “the environmental conditions might not be conducive to its spread,” but the virus is “not going to have a hard time finding people to infect,” Adalja said.

Dr. George Rutherford, an epidemiologist and infectious disease expert at UC San Francisco, also warned against pinning too much hope on a sharp warm-weather slump. After all, he said, the virus was circulating in the Southern Hemisphere in January, which was the height of summer there.

“So that’s one strike against it,” he said.

A second strike, he added, comes from a report of likely coronavirus transmission at a bathhouse about 430 miles from Wuhan, China.


A customer who had been to Wuhan visited the facility in January, a day before he developed symptoms of COVID-19. Seven other customers who used the same shower, sauna and swimming pool were subsequently infected, as was an employee. The virus seems to have been able to spread even though temperatures in the bathhouse ranged from 77 to nearly 106 degrees Fahrenheit, and humidity was as high as 60%, according to the report in the journal JAMA Open Network.

“If it transmitted there, there’s not a lot of hope for the summer,” Rutherford said.

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Humans could make things even easier for the coronavirus if they relax social distancing measures and other restrictions too hastily, said Dr. Robert Kim-Farley, a medical epidemiologist and infectious disease expert at UCLA.

“It’s possible that this second wave won’t even wait until the fall — it could be that simply we relax our physical distancing too soon,” said Kim-Farley, who led the Los Angeles County Department of Public Health’s Division of Communicable Disease Control and Prevention for 14 years.

“We may have to, from time to time, reimpose a few physical distancing measures to make sure that we continue to beat it back,” he added.

Keep in mind, the coronavirus outbreak began in the United States partway through a typical cold and flu season, which begins in the fall. If the virus resurges, it will have more time to spread under more hospitable conditions.

That said, the next seasonal peak for other coronaviruses is still several months away, experts said. How we use those months could make all the difference between whether a second wave can be managed or will make the losses we’ve seen so far seem small by comparison.


To prepare, health officials must make coronavirus testing — both to diagnose active infections and to identify people who have recovered — more robust and widespread. With a better handle on how many people have survived the infection, scientists can more accurately determine SARS-CoV-2’s transmission patterns, the possible level of herd immunity and where communities are on the epidemic curve.

The national strategic stockpile of personal protective equipment will need to be replenished, as will states’ own stockpiles of ventilators and other necessary medical equipment. Hospitals must develop surge capacity plans and be ready to implement them.

The goal, Kim-Farley said, is to ensure “that we don’t get blindsided the second time around.”

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There’s also a chance that, in the intervening months, researchers will be able to identify treatments that are at least somewhat effective for COVID-19 patients, he added. (A coronavirus vaccine is likely to take a year or more to develop, experts have said.)

These preparations will be crucial, Kim-Farley said, because COVID-19 will probably be around during the entire 2020-21 influenza season — and it’s difficult to predict how bad any given flu season will be. The 2011-12 flu season, for example, saw about 9.3 million cases and 12,000 deaths, for instance, while the 2017-18 season saw about 45 million cases and 61,000 deaths, according to the CDC.

Either way, an influx of seriously ill COVID-19 patients on top of the usual seasonal influenza patients could swamp hospitals and raise the risk of patient deaths.


That’s why it will be more important than ever to get the flu vaccine, Kim-Farley said. Raising the level of community immunity to seasonal influenza may not reduce the spread of the coronavirus, but it will reduce the odds of being inundated by two outbreaks at once.

“I think we need to be prepared for the worst and hope for the best,” Kim-Farley said.