Temperature and latitude are not associated with the spread of the COVID-19 disease, say researchers, adding that they found a weak association between humidity and reduced transmission.
The results — that hotter weather had no effect on the pandemic’s progression — surprised the authors. “Our study provides important new evidence, using global data from the COVID-19 epidemic, that these public health interventions have reduced epidemic growth,” said study researcher Dr Peter Juni from the University of Toronto, and St Michael’s Hospital in Canada.
The study, published in the Canadian Medical Association Journal, looked at 144 geopolitical areas — states and provinces in Australia, the US and Canada as well as various countries around the world — and a total of more than 3,75,600 confirmed COVID-19 cases. China, Italy, Iran and South Korea were excluded because the virus was either waning in the case of China or in full disease outbreak at the time of the analysis in others.
To estimate epidemic growth, researchers compared the number of cases on March 27 with cases on March 20, and determined the influence of latitude, temperature, humidity, school closures, restrictions on mass gatherings and social distancing measured during the exposure period of March 7 to 13.
They found little or no association between latitude or temperature with epidemic growth of COVID-19 and a weak association between humidity and reduced transmission. “We had conducted a preliminary study that suggested both latitude and temperature could play a role. But when we repeated the study under much more rigorous conditions, we got the opposite result,” Juni said. The researchers did find that public health measures, including school closures, social distancing and restrictions of large gatherings, have been effective.
“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,” Juni added. According to the research team, summer is not going to make this go away.