As COVID-19 began infecting thousands across the globe, many anxiously awaited the start of warmer weather in hopes that rising temperatures would help to diminish the spread of the virus. Alas, that will not be the case, as researchers at the University of Toronto’s Dalla Lana School of Public Health and Faculty of Medicine were able to determine in a peer-reviewed study that heat has little to no bearing on how COVID-19 spreads.
“It’s very unlikely that temperature plays a role in the dynamics of the epidemic of COVID-19. It will not play a role, what we saw was a flat line, there is no association between temperature and epidemic growth,” said Dr. Peter Jüni of St. Michael's Hospital, the study’s lead author and a professor at the University of Toronto.
During a talk on March 5th, Dr. Jüni had mentioned that seasonality would likely play a factor in helping mitigate the effects of COVID-19, but a remark from a student made him think otherwise.
“A gentleman from the audience asked me, if there was seasonality ‘why would Singapore struggle as well?’ The person triggered me to think about it,” he said.
At the time, Singapore was experiencing temperatures in the low-to-mid 30s with a relative humidity around 80 per cent and peaking at 96 per cent, but the country was seeing cases rise and even hit 1,000 positive tests a week.
Following a come-to-light moment, Dr. Jüni got his cohorts in order and organized a study invoking the help of eight scientists, including data collectors, a statistician and an epidemiologist who evaluated 144 areas worldwide which had at least ten cases and had experienced local transmission by March 20, 2020.
With the spring equinox around the corner on March 20, Dr. Jüni figured it would be the perfect time, as the centre of the visible sun is directly above the equator and the amount of sunlight serves as a proxy for heat and humidity.
“We just tried to answer this question as a rapid response as reliably as possible, it was still challenging, if we wait and do this conventionally — it would be too late,” he said.
As word of this study began to be talked about amongst his colleagues, Dr. Jüni was stunned at how many of them had preconceived notions that humidity and heat would likely have a positive effect in reducing the viral nature of COVID-19.
“It’s spring, it’ll be summer soon, it’s going to slow down, we all just believed that. I had colleagues who told me when I was recruiting for the trial that the tests will probably just decrease the growth,” he said.
As headlines of the virus being gone by summer circulated widely, Dr. Jüni thinks many people including scientists were drawing parallels of COVID-19 to the flu and how limited the spread of infection is during summer.
“What the big difference between this virus and the flu is that all of us have partial immunity against the flu, we all once experienced the flu and some or most of us get vaccinated,” he said.
However, though there is a lot of belief that heat diminishes the effects of the common flu, Dr. Jüni said there isn’t concrete evidence that heat is the sole reason why the flu isn’t as strong during the summer.
“For the flu we don’t know all the reasons why it goes away, it’s very possible that temperature and humidity play a role,” he said. “There’s summer break, it’s school closures and when schools open again, the flu comes back, so how much of a factor is that, we just don’t know.”
Forget the heat, don’t open ‘all at once’
With humidity and heat having little effect in the results section of their study, Dr. Jüni and his fellow authors concluded public health measures such as physical distancing, school closures and limiting mass gatherings had a very strong effect.
“In a multivariable model, there was a strong association with the number of implemented public health interventions whereas the association with absolute humidity was no longer significant,” they wrote in the study.
As the study evaluated global trends, they discovered that countries which were quick to implement physical distancing and other public health measures before the official declaration of the pandemic didn’t experience major jumps in positive cases.
“Areas that had implemented this by March 11 faired consistently better than areas that hadn’t done it at that time,” said Dr. Jüni.
While nearly all the Canadian provinces have announced measures to reopen their economies and societies, Dr. Jüni notes that a segmented and slow approach will serve best at ensuring there is no second wave.
“The politicians and administrators need to be very careful about lifting restrictions in steps and in a smart way, it can’t happen all at once,” he said.
The responsibility doesn’t fall solely on the government’s shoulders either, as Dr. Jüni notes that places that have been successful with their reopening are still following similar measures. He insisted that schools cannot open the same as before and they will need to limit class sizes to 15 and stagger timing of classes.
“I hope people are very careful when restrictions are lifted, everyone one of us needs to be very responsible to adhere to principles of physical distancing, we cannot go back to the old normal,” said Dr. Jüni. “There is no old normal for sometime.”
With timely completion of this research, Dr. Jüni hopes people gain a better understanding of COVID-19 going forward and how restrictions have had a positive impact.
“Summer won’t come to our help, so we need to. The public health interventions seem to work to a large effect,” he said.