  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.
