Researchers at UCSB studied the effect of UV exposure on COVID-19 transmission globally and found that the virus may be sensitive to UV light.
The results can guide seasonal responses to COVID-19, though temperature, humidity and precipitation are also seasonal factors.
“Related species of coronavirus — like SARS from 2003 and MERS from 2012 — turned out to have weak relationships with temperature and humidity, but were sensitive to UV radiation,” said Dr. Kyle Meng, study co-author and environmental economist at UCSB.
Dr. Tamma Carleton, also an environmental economist at UCSB’s Bren School, and researchers from Harvard and France’s École Normale Supérieure Paris-Saclay co-authored the paper alongside Dr. Meng. The research is published in the Proceedings of the National Academy of Sciences.
They had to be intentional with their choice of dataset in order to avoid results contaminated by other factors, such as health care quality, governmental protocols and cultural norms.
They chose to look at daily COVID-19 cases across the globe and each country’s daily UV exposure, allotting for a lag between the onset and detection of the virus.
“We basically ask whether daily fluctuations in environmental conditions experienced by a population affect new COVID-19 cases up to two weeks later,” Dr. Meng said.
Researchers compiled a global dataset of over 3,000 spatial units, matched its meteorological conditions and analyzed four variables: UV radiation, temperature, humidity and precipitation.
They found that UV exposure had a significant correlation to a decrease in COVID-19’s spread.
An increase in UV exposure by one standard deviation (approximately the difference in UV light between May and June in Los Angeles) reduced the growth rate by around one percentage point over the following two weeks.
The transmission rate is affected much more by social distancing policies and closures, the authors noted.
The researchers noticed cases increase when restrictions loosened in summer months, though UV radiation was at its highest. Looking at the daily differences helped them still see UV’s impact.
“This is a big reason why our study uses daily fluctuations in UV exposure, in part to avoid conflating influences when looking at long-term, varying fluctuations,” Dr. Meng said.
The findings are consistent with the current surge in infections. But more precise data is needed to research other seasonal variants.
“We are confident of the UV effect, but this is only one piece of the full seasonality picture,” Dr. Carleton said.
Lab studies can isolate the factors. But prior knowledge in areas like biology also helped the researchers form a conclusion.
“Just as UV can destroy our own DNA if we don’t use sunscreen, UV can damage the COVID-19 virus,” Mr. Proctor said.
Behavioral patterns also factor into the transmission. Like, when it is sunny outside, people may opt to spend more time outdoors.
Lab studies and population-level studies will help researchers get a better picture of seasonal impacts.
“In the context of all this, our study suggests that seasonal changes in UV may influence COVID-19 transmission in the coming months,” Dr. Meng said. “And if that’s true, we need to think carefully about how to modulate COVID-19 containment policies in a seasonal manner.”