Tall building with sun and bright blue sky above, used to explain COVID-19 and its relationship with heat

Why COVID-19 got worse, not better, in the summer heat

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August is known for its sweltering heat and triple-digit temperatures — this year, many had hoped it would offer something else, too: relief from COVID-19.

But the virus is rampant this summer. Can warm weather really help stop the spread of infection as we were told?

There’s a good reason some had hoped that warm weather might stop the novel coronavirus in its tracks. Cold viruses and the flu tend to be seasonal and abate during the summer.

“It’s an enticing idea that the same would apply to the pandemic,” says Leslie Cler, MD, FACP, CPE, chief medical officer for Methodist Dallas Medical Center. “After all, the protective coating of the coronavirus — commonly found among some pathogens — seems to weaken with changes in heat and humidity. But this doesn’t seem to be the case with COVID-19. So far, we have seen surges of infections in many parts of the United States.”


Texas saw record new cases and fatalities in July.

One factor could be that more people are spending time indoors, looking to get away from the intense heat. And in a public setting, such as a restaurant or coffee shop, that’s especially troubling since it can force strangers in closer proximity than is safe, allowing the coronavirus to spread more easily through respiratory droplets or even the air.

According to a report by The Harvard Gazette, people are more likely to be “rebreathing air in the room and from each other” in a space with closed windows and air conditioners turned on.

It’s the same theory of why the flu hits hardest in the fall and winter — when cold weather forces people to stay indoors.

But there are other things that set this virus apart from other seasonal respiratory viruses, Dr. Cler says.


“The reason our bodies recover from other respiratory illnesses stems from the immunity we gain from prior exposure or vaccinations,” Dr. Cler says. “That, in combination with the heat and humidity, can impede the spread of those viruses in warmer weather. Our population does not have the immunity to the coronavirus in the same way.”

Without a vaccine, it’s harder to achieve herd immunity, which protects the wider community once a majority becomes immune to the disease. An added complication is that those who have already contracted COVID-19 could be reinfected if their antibodies fade.


Another difference is that illnesses like the common cold and influenza are more familiar to us, and doctors have years of experience treating them.

“We have a sense of the risk of transmission and expected rates of infection, even by season,” Dr. Cler says.

By comparison, COVID-19 hasn’t been around for long, and researchers are still trying to gauge its infection rate and risk factors. Even with data being collected daily, it’s not easy to predict the path this outbreak will take, according to the National Academy of Sciences.

“To say it looks one way in winter and another way in summer might be a bit speculative since no country or region has experienced years of this, so there are no patterns by which to judge,” Dr. Cler says.

Woman wearing mask and apron opening up doors to bar/restaurant, used to explain COVID-19 and its relationship with heat


As businesses welcome customers and workplaces continue to reopen, it’s easy to pretend life is back to normal. But letting down our guards would be a mistake, and we should all take precautions to protect ourselves and each other.

“Wearing masks, social distancing, and sheltering in place have been the factors most responsible for slowing transmission in areas where surges subsided,” Dr. Cler says. “Those are things that everyone can work on, and they do make a difference.”

Without these interventions, communities will continue seeing a spike in cases, which can overwhelm healthcare workers and hospitals.

But Dr. Cler does see one hopeful prospect on the horizon.

“Vaccine efforts appear to be going well, with promising progress from multiple trials,” he says. “It remains our best hope for getting past this pandemic as soon as possible.”

Keep cool from the heat and stay safe from COVID-19 this summer.