As much of the country looks forward to the possibility of rubbing shoulders again in summer, scientists are carefully watching for signs that the coronavirus transmission could slow in warm weather.
The consensus seems to be that the virus will be seasonal and endemic, meaning that, like the common cold, it will thrive in winter but will likely never go away. That doesn’t mean the United States will be in the clear come June.
“It is possible, that given how new the virus is and the number of people who are still susceptible, we may continue to see this virus spread even over the summer months, though at a lower level than the first wave, before returning for a second fall peak,” said Robert A. Bednarczyk, a global health professor at Emory University, by email.
Some researchers say it’s too early to tell if actual physical conditions, such as warmer, more humid air, or natural social distancing that comes with more time outdoors will throttle the spread of COVID-19.
“We haven’t lived with this virus or it with us long enough to actually observe what happens as the seasons change,” said Dr. David A. Relman, a professor at the Stanford University School of Medicine, adding that the virus that causes COVID-19 was first detected in December.
In an exclusive interview, Paul Dabisch, a senior research scientist at the Department of Homeland Security’s biodefense research laboratory, said that initial lab tests show sunlight, higher temperatures and humidity are hurdles for the survival of the coronavirus.
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“What we have found so far is that sunlight seems to be very detrimental to the virus,” he said.
William Bryan, the acting undersecretary for science and technology at Homeland Security, said during a White House briefing April 23, “The virus is dying at a much more rapid pace, just from exposure to higher temperatures and just from exposure to humidity.”
An analysis in Swiss Medical Weekly found that “seasonal variation in transmissibility has the potential to modulate” the spread of the coronavirus.
“I think it is highly likely that it will show winter peaks in temperate areas of the world,” co-author Jan Albert of Sweden’s Karolinska University Hospital said by email.
But even with that finding comes caution: “The onset of spring and summer could, for example, give the impression that (the coronavirus) has been successfully contained, only for infections to increase again in 2020-2021 winter season,” the Swiss Medical Weekly paper said in March.
Other studies have drawn correlations between cooler climes and higher transmission rates, but socioeconomic factors can also be at play, including the quality of health care, underlying health conditions and social distancing protocols in a particular region, Relman said.
Although the coronavirus may not survive as well on laboratory surfaces in warmer, more humid weather, it might still be easily transmitted from person to person, the experts said.
Albert said the coronavirus “will become endemic” like the four strains associated with the common cold.
“Given the magnitude of the global spread, it is hard to see that it will be contained and disappear,” he said. “It is likely that it will become a fifth endemic coronavirus.”
Dr. Arnold S. Monto, an epidemiology professor at the University of Michigan’s School of Public Health, argued there’s little evidence so far that this coronavirus will act like its endemic relatives and take a summer break.
“This pandemic virus is behaving differently,” he said by email. “The common viruses rarely cause severe disease, so we are not sure if they will behave similarly.”
As such, people should not expect to relax their precautions much in warmer months.
“It is important that individuals still do what they can to protect themselves and others, including wearing masks, washing their hands and maintaining appropriate physical distances,” said Bednarczyk of Emory University in Atlanta.
Stanford’s Relman said: “It may turn out the summer is a better time, but we don’t want to wait and hope and find out we’re wrong. It’s much more wise to say, ‘Let’s not count on it.'”
Dennis Romero writes for NBC News and is based in Los Angeles.
