For the Canadian researchers, the finding that hotter weather doesn’t reduce COVID-19 cases was surprising.
“We had conducted a preliminary study that suggested both latitude and temperature could play a role,” said study co-author Dr. Peter Jüni, also from the University of Toronto. “But when we repeated the study under much more rigorous conditions, we got the opposite result.”
But Dr. Amesh Adalja, a senior scholar at the Johns Hopkins Center for Health Security in Baltimore, said there are reasons why summer might not make a dent in COVID-19 infection rates.
“Because this is a novel virus, without population immunity, we can’t expect to see a full suppression of transmission based on seasonality,” he explained. “Though certain environmental conditions might be less conducive to spread from surfaces during summer months, the sheer fact that so many people are susceptible may not make as much of a difference because person-to-person spread will continue.
“It will be important that even in the summer months, states remain vigilant regarding the number of cases that are occurring with full situational awareness of the rate of hospitalizations, to prevent hospitals from going into a stress mode of functioning,” Adalja noted.
In the Canadian study, researchers compared the number of confirmed cases of COVID-19 in the United States, Canada and other countries on March 20 and again on March 27, to determine the effect of latitude, temperature, humidity, school closures, restrictions of mass gatherings, and social distancing on the spread of the disease. They looked at a total of more than 375,600 confirmed COVID-19 cases.
The results showed little or no association between latitude or temperature with a rise in COVID-19 cases and a weak association between humidity and fewer cases.
But school closures, social distancing and restrictions of large gatherings have helped control cases, according to the researchers.
“Our study provides important new evidence, using global data from the COVID-19 epidemic, that these public health interventions have reduced epidemic growth,” Jüni said in the release.
“Our results are of immediate relevance as many countries, and some Canadian provinces and territories, are considering easing or removing some of these public health interventions,” he added.