A new study has poured cold water on the idea that hotter weather will slow or stop the spread of coronavirus, analysing data from around the world.
Researchers in Canada analysed data from 144 geopolitical areas from Australia to Canada, examining more than 376,000 confirmed COVID-19 cases.
They found that hotter temperatures made little or no difference to the spread of the virus, but that social distancing measures were highly effective in stemming its spread.
"Summer is not going to make this go away," says Professor Dionne Gesink, epidemiologist at Dalla Lana School of Public Health at the University of Toronto.
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"It's important people know that. On the other hand, the more public health interventions an area had in place, the bigger the impact on slowing the epidemic growth.
“These public health interventions are really important because they're the only thing working right now to slow the epidemic."
To estimate epidemic growth, researchers compared the number of cases on 27 March with cases on 20 March.
Researchers calculated the influence of latitude, temperature, humidity, school closures, restrictions of mass gatherings and social distancing measured during the exposure period of 7 to 13 March.
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.
The results that hotter weather had no effect on the pandemic's progression surprised the authors.
"We had conducted a preliminary study that suggested both latitude and temperature could play a role," said lead author Dr Peter Jüni, of St Michael’s Hospital and the University of Toronto. "But when we repeated the study under much more rigorous conditions, we got the opposite result."
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," said Dr Jüni.
The authors note several study limitations, such as differences in testing practices, the inability to estimate actual rates of COVID-19 and compliance with social distancing.