News and stories Based on Science Does the spread of COVID-19 slow down when the weather is warmer?

Does the spread of COVID-19 slow down when the weather is warmer?

Based on Science

Some viruses vary by season, while others don’t. It is not yet known whether SARS-CoV-2, the coronavirus that causes COVID-19, is affected by the change in seasons.

Health and Medicine

Pandemics

Weather

Last update April 15, 2020

Viruses can be seasonal—or not—for many different reasons.

Air temperature and humidity affect how some viruses spread. For example, influenza spreads more quickly in drier and colder conditions. For other viruses, temperature and humidity do not affect disease transmission.

In some cases, a disease’s seasonality may have more to do with changes in human behavior—attending school and spending more time in crowded indoor spaces, for example—than with the weather itself. A virus's spread and impact may also be affected by seasonal changes in people’s immune systems or changes in the number of susceptible people in the population.

It's unclear which, if any, of these reasons will apply in the case of SARS-CoV-2, the novel coronavirus.

It’s still too early to tell if the novel coronavirus is affected by seasonal changes.

Since the pandemic began, warmer weather and more humid conditions have not been enough to slow the spread of COVID-19. People have been infected with SARS-CoV-2 around the world, no matter the season.

SARS-CoV-2 is a new virus in humans, so no one was immune to it when the pandemic started. Even if the virus spreads more slowly in warmer seasons, the large number of susceptible people means infections continue to grow even when the temperature is hotter and humidity is higher.

It may be that as more people get immunity to the virus, either by recovering from an infection or by getting vaccinated, outbreaks will become more seasonal, like we see for the flu. But we still don’t know.