Sunny days are associated with higher rates of COVID-19, likely because they tempt more people outdoors, putting them at increased risk of infection, researchers say.
But they also found that higher heat and humidity may slow the spread of COVID-19.
And they said their study might shed light on how different seasons may affect the spread of the disease.
“There is a lot of pressure to reopen the economy, and many people want to know if it will be safer to do so in the summer months,” said study lead author Antonio Páez. He’s a professor and researcher in the School of Geography and Earth Sciences at McMaster University in Ontario, Canada.
“Restrictions in movement, which have begun to ease around the world, hinge in part on how SARS-CoV2 will be affected by a change in season,” Páez said in a university news release.
Previous research has shown that viruses such as influenza and SARS thrive in lower temperatures and humidity, but little is known about how weather affects SARS-CoV2, the virus that causes COVID-19.
To learn more, Páez and his international team of colleagues assessed the link between weather and the spread of COVID-19 in several provinces in Spain. That country is among the hardest hit by COVID-19, with more than 270,000 cases.
At higher levels of heat and humidity, every percentage increase was associated with a 3% decrease in the incidence of COVID-19, possibly because the coronavirus is less likely to survive in warmer temperatures.
However, sunnier days were associated with higher rates of the disease, likely because lockdown measures are ignored by many people on such days, according to the authors.
They also found that transmission rates fell in locations with greater population density and in those with more older adults, suggesting that people in these areas believe they’re at greater risk and therefore more likely to adhere to lockdown rules.
“We will likely see a decrease in the incidence of COVID-19 as the weather warms up, which is an argument for relaxing social distancing to take advantage of the lower incidence associated with higher temperatures,” Páez said.
“But a more conservative approach would be to use the months of summer to continue to follow strict orders to remain in place and to crush this pandemic,” he added.
The study was published online in the journal Geographical Analysis.
The U.S. Centers for Disease Control and Prevention has more on COVID-19.