Ultra Violet radiation from sunlight: A key moderating factor in the spread of SARS-CoV-2 during the pandemic of 2020

Lockdowns imposed in most of the countries were lifted following a decline in the COVID-19 cases towards May-June 2020. A recent surge (second wave) in the COVID-19 cases in Europe and other temperate countries as compared to the tropical regions suggests the likely role of solar radiation. We hypothesized that ultraviolet radiation's effect might be a significant factor moderating the spread of the COVID-19 across countries. Regression analysis was done for the UV radiation data for seven hotspot cities (New Delhi, Mumbai, Milan, Madrid, New York, Melbourne and Sydney) with the daily COVID-19 cases. Global erythemal UV radiation values were lower during winter and higher during summer. In general, the daily new COVID-19 cases registered were higher during the winter months having low UV radiation dose (0.5-3.7 kJ m-2). Cases began to decline with summer onset that corresponded to increased UV radiation (2.5-6.7 kJ m-2). Our studies suggest that the natural UV radiation could be a strong determining factor moderating the spread of COVID-19 cases. The importance of UV radiation in natural sunlight as a disinfectant for SARS-CoV-2 cannot be ignored since the lockdowns were lifted; further, it can be considered as a factor for COVID management.