Some research suggests that the novel coronavirus does not survive in the heat. But what does that mean for the summer?

By Korin Miller
Updated April 22, 2020
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About a month deep into #quarantinelife, many people have a huge question on their minds: When will the coronavirus (COVID-19) pandemic be over? And, if it's not possible to seriously contain the virus before a vaccine is available, will COVID-19 slow down in summer, at least?

It's important to point out that COVID-19 is still a newly discovered virus that hasn't been previously identified in humans. And, with that, researchers are still learning how the novel coronavirus behaves, including how it copes with changing seasons.

Still, there are some theories on what to expect, based on what experts have seen from other coronaviruses, seasonal influenza, and the common cold. "Other coronaviruses besides the one that causes COVID-19 still spread in the summer, albeit less so than in the colder months," says Richard Watkins, M.D., an infectious disease physician in Akron, Ohio, and a professor of internal medicine at the Northeast Ohio Medical University. (Related: Everything You Need to Know About Coronavirus Transmission)

But whether this will be the case for COVID-19 is unclear at this point. After all, severe acute respiratory syndrome (SARS), the coronavirus that spread to more than 8,000 people around the world in 2003, is "much less infectious than COVID-19," according to the World Health Organization (WHO). More specifically, COVID-19 appears to be three times more infectious than the seasonal flu, Robert Redfield, M.D., director of the Centers for Disease Control and Prevention (CDC), recently told NPR.

COVID-19 clearly isn't the same as influenza, the common cold, or other coronaviruses that scientists are a little more familiar with, but some recent data could provide clues about what's ahead for summer. Here's what you need to know.

Can coronavirus surivive in heat?

Some emerging research suggests that yup, heat can kill SARS CoV-2, the virus that causes COVID-19. But it's more complicated than warmer weather = grab your beach towel and screw social distancing recommendations.

A recent preliminary report published online in BioRxiv (that hasn't been peer-reviewed yet) found that researchers in France had difficulty killing the virus with high heat—like, much higher heat than you'd experience IRL. For the study, the researchers infected African green monkey kidney cells with the novel coronavirus and placed the infected cells in a 140-degree Fahrenheit room. The virus survived in the cells, even when it was exposed to that 140-degree heat for an hour. Scientists finally managed to torch the virus when it was exposed to 197.6-degree heat for 15 minutes, according to the report.

Since this research was done with animal cells rather than human cells, in a controlled lab setting no less, it's tough to say whether the findings might apply to the real world. Plus, summer temperatures obviously never get that hot IRL. However, the study authors pointed out that most people infected with COVID-19 have a lower viral load than that of the monkey cells. (Viral load is essentially the total amount of virus a host has inside them; the lower someone's viral load, the less infectious they are.) As a result, it's possible that lower temperatures could kill SARS CoV-2 in the context of human cells—but that's just speculation at this point, the researchers wrote.

Another early analysis published by researchers at MIT (which also hasn't been peer-reviewed yet) found that, to date, 90 percent of confirmed COVID-19 cases have happened in countries with a temperature range of 37 to 63 degrees Fahrenheit. The researchers acknowledged that tropical countries haven't tested for COVID-19 as often as their counterparts that have experienced cooler temperatures during the pandemic, which could certainly skew their findings. However, the study authors also said that warmer countries like Australia, the United Arab Emirates, Qatar, Singapore, Bahrain, and Taiwan have done "extensive testing" of their populations, and their per capita cases of COVID-19 are lower than those in the U.S. and several European countries. Basically, the virus seems to be spreading more slowly in warmer climates, the researchers wrote. "Our results in no way suggest that [COVID-19] would not spread in warm humid regions and effective public health interventions should be implemented across the world to slow down the transmission of [COVID-19]," the study authors concluded. (Related: Can Steam Kill Viruses?)

Finally, a Department of Homeland Security (DHS) briefing leaked to Yahoo News cited unpublished research that suggests the risk of COVID-19 transmission from outdoor surfaces may be lower during daylight and under higher temperatures and humidity. "Sunlight destroys the virus quickly," reads the briefing, according to the news outlet. "Outdoor daytime environments are lower risk for transmission."

It sounds promising for summer, but the report also warned that the research doesn't indicate that summer weather will wipe out, or even slow down, new cases of the coronavirus.

So, will warm weather slow down coronavirus?

TBH, it's still unclear. "The hope that the SARS CoV-2 virus will go away this summer is purely hope at this time," says David Cennimo, M.D., assistant professor of medicine-pediatrics infectious disease at Rutgers New Jersey Medical School. "We won't know for a while."

But again, plenty of other respiratory viral infections are seasonal, and there are some helpful theories on why that's the case, says Dr. Cennimo. One is that people tend to be in closer quarters in winter, "so it is easier for infectious droplets to hit others," he explains. Also, high humidity in warmer seasons makes respiratory droplets heavier, causing them to fall faster rather than linger in the air (meaning fewer opportunities to spread), says Dr. Cennimo. In theory, the same would be true for the virus that causes COVID-19, but experts just don't know yet.

Some pathogens are also susceptible to UV light, "so brighter sunlight may inactivate them faster," explains Dr. Cennimo, adding that it's not yet proven if this is true for COVID-19. "Heat can certainly [alter] viruses," but this may be irrelevant given the normal range of warm temperatures in typical weather patterns, he notes.

There's also a theory floating around on the internet that the vitamin D boost you get from summer sunlight can help strengthen your immune system to better fight COVID-19. But experts say there's not much evidence to back that up at this point. "Vitamin D has been shown to be beneficial in bacterial infections, and low vitamin D can increase susceptibility for infection," explains Dr. Cennimo. "But there are fewer data to suggest that vitamin D plays a role in viral immune function."

"The role of vitamin D in preventing or mitigating the symptoms of COVID-19 is an interesting but an as-yet-unproven hypothesis," adds Dr. Watkins. (Related: The Low Vitamin D Symptoms Everyone Should Know About)

Ultimately, it's "difficult to predict" if there's any chance of COVID-19 slowing down in the summer, "especially since the virus is known to be spreading in warm areas of the world, like Africa," explains Dr. Watkins.

And even if COVID-19 does slow down in the summer, Dr. Cennimo says he's "very concerned" that the virus will come back in the fall anyway. In fact, CDC director Dr. Redfield recently raised concerns about the virus's potential return next winter—and what that might look like if it coincides with the start of flu season. "There's a possibility that the assault of the virus on our nation next winter will actually be even more difficult than the one we just went through," Dr. Redfield told The Washington Post, noting that the combination of COVID-19 and flu season could overwhelm healthcare systems even further.

Bottom line: For now, it's really best to keep up with known ways of lowering your COVID-19 risk, like washing your hands regularly, maintaining social distancing, and disinfecting your personal belongings—regardless of the weather or season, says Dr. Cennimo.

"Many experts believe the spread of COVID-19 will decrease, but not end in the summer," says Dr. Watkins. Still, it's really hard to say at this point. "This is a newly introduced pathogen, so we really do not know," says Dr. Cennimo.

The information in this story is accurate as of press time. As updates about coronavirus COVID-19 continue to evolve, it’s possible that some information and recommendations in this story have changed since initial publication. We encourage you to check in regularly with resources such as the CDC, the WHO, and your local public health department for the most up-to-date data and recommendations.

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