Covid-19 spreads faster during winters when it’s dark with low UV levels: Study

Prashasti Awasthi Mumbai | Updated on December 18, 2020

Changes in UV between winter and summer led to a 7% point decrease in the Covid-19 growth rate

A new study stated that ultraviolet radiations are inversely proportional to Covid-19 viral load.

The study, published in the journal PNAS, suggested that the incidence of Covid-19 may have a seasonal pattern in which the virus spreads faster in the winter when it’s darker with lower levels of UV radiation than during summer.

Jonathan Proctor, a co-author of the study from Harvard University in the US said in a statement, “Understanding the potential seasonality of Covid-19 transmission could help inform our response to the pandemic in the coming months.”

For the study, scientists analysed daily Covid-19 and weather data from over 3,000 administrative regions in more than 170 countries. They found that the spread of Covid-19 is lower during the weeks when there was a higher UV exposure.

However, the researchers said that they still have not figured out how this phenomenon works due to the scarcity of data. “We basically ask whether daily fluctuations in environmental conditions experienced by a population affect new Covid-19 cases up to two weeks later,” said study co-author Kyle Meng from the University of California Santa Barbara in the US.

For this study, they collected the data during the initial stage of the pandemic and added information as the pandemic passed through the year.

They found that changes in UV between winter and summer led to a 7-percentage point decrease in the Covid-19 growth rate on average across the Northern Hemisphere.

The researchers speculated that this could also happen due to the change in atmospheric pressure and precipitation. “We are confident of the UV effect, but this is only one piece of the full seasonality picture,” said Jules Cornetet, another co-author of the study.

However, the scientists cautioned that UV exposure alone is unlikely to stop the spread of the virus without strong social distancing policies.

“Regardless of the weather, additional measures appear to be necessary to substantially slow the spread,” Proctor said. The researchers added that it is also unclear what mechanism is driving this effect.

Published on December 18, 2020

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