Can summer lead to a slowdown of the coronavirus epidemic?

Many in the Northern Hemisphere have been hoping that would be the case with COVID-19, considering that’s what usually happens with influenza and seasonality. Unfortunately, we may not be so lucky.

A new, thorough study carried out by Canadian researchers found no connection between temperature or latitude and the spread of the virus.

“We had conducted a preliminary study that suggested both latitude and temperature could play a role,” said the University of Toronto health policy researcher Peter Jüni in a statement. “But when we repeated the study under much more rigorous conditions, we got the opposite result.”

The researchers collected data from 144 geopolitical areas that registered at least 10 positive cases of coronavirus. In Australia, the US, and Canada, they analyzed data at the state, territory, and province level, while in the rest of the world, they looked at the country-level data.

They then compared the case count on 27 March to the case count reported 7 and 14 days earlier, investigating changes in temperature, latitude, humidity as well as any social restrictions such as school closures in the areas analyzed. They excluded countries that, by March, had a nation-wide outbreak (such as China).

The results were quite revealing: there seemed to be no clear correlation between temperature and disease spread.

While no link was seen by the researchers between the expansion of coronavirus and latitude and temperature, social restrictions and public health interventions were found to be highly important to reduce epidemic growth.

“Coronavirus doesn’t need favorable conditions to expand. We are highly confident on our results, the temperature or the weather overall won’t have any effect,” said Jüni to EFE news agency. “Maybe the humidity will have an effect on the spread of the virus, but will be very small and won’t be sufficient to slow it down.”

Previous studies seemed to suggest that hot, humid weather seems to slow down the virus somewhat — but according to this study, that’s not the case. The new findings are also in line with three studies from China that previously reported no evidence for an association of epidemic growth with temperature and relative humidity, but strong decreases in epidemic growth associated with public health measures — highlighting the importance of suppression strategies.

For co-author Dionne Gesink, summer “is not going to make” the coronavirus epidemic disappear.

“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,” she said.

The researchers noted several study limitations. Because of considerable differences in testing practices between different geopolitical areas, the actual rates of COVID-19 could not be reliably estimated. The team couldn’t identify reliable information on the number of SARS-CoV-2 tests per million inhabitants.

Nevertheless, the study can be very relevant, especially as countries start easing or removing restrictions. And it gives a special message to US President Donald Trump, who in February had said the coronavirus would go away with higher temperatures – not likely based on the findings.

The study was published in the Canadian Medical Association Journal.