The model that the research is based upon finds that the incidence of coronavirus transmission is linked to a seasonal pattern, in terms of transmission occurring faster in the winter than in the summer. While there are different reasons why a virus might spread more rapidly in the winter (something that mirrors influenza spread), the levels of darkness appear to be a contributing factor.
Harvard University researchers have drawn this inference by examining weather patterns from some 3,000 administrative regions located in more than 170 countries. Crunching these data, it was revealed that the spread of the SARS-CoV-2 virus through a given population tended to be lower in the weeks following higher ultraviolet light exposure.
This association appears to tally with some emerging studies that show how UV light, when applied to a surface, can inactivate coronaviruses. The sensitivity of the UV appears to be a key factor, with the wavelength 267 nm ~ 279 nm being optimal. As well as surface treatment, the application of UV-C light to ventilation systems, and water systems in hospitals, is being explored.
Inactivation by UV could occur via several mechanisms, among them damage to nucleic acids, proteins, or internal production of oxygen radicals.
The researchers found that changes in UV between winter and summer resulted in a 7-percentage point decrease in the coronavirus transmission rate within the Northern Hemisphere. However, it remains that the complete seasonality of COVID-19 remains unclear and further research is required. This is due to the uncertain role of other variables, like temperature and humidity.
Importantly, while seasonal changes in UV appear to alter the spread of COVID-19 this is not as much as achieved by social distancing. As seen during the summer, coronavirus infections still remain high in crowded places and especially in relation to indoor environments. Therefore, standard COVID-19 avoidance measures should continue to be practiced.
The research findings have been published in the journal Proceedings of the National Academy of Sciences. The research paper is titled “Global evidence for ultraviolet radiation decreasing COVID-19 growth rates.”
