A delayed modulation of solar ultraviolet radiation on the COVID‐19 transmission reflects an incubation period

Laboratory experiments have revealed the meteorological sensitivity of the coronavirus disease 2019 (COVID‐19) virus. However, no consensus has been reached about how outdoor meteorological conditions modulate the virus transmission as it is also constrained by non‐meteorological conditions. Here, we identify the outbreak's evolution stage, constrained least by non‐meteorological conditions, by searching the maximum correlation coefficient between the ultraviolet flux and the growth rate of cumulative confirmed cases at the country level. At this least‐constrained stage, the cumulative cases count around 1300–3200, and the count's daily growth rate correlates with the ultraviolet flux and temperature significantly (correlation coefficients r = −0.54 ± 0.09 and −0.39 ± 0.10 at [Formula: see text] , respectively), but not with precipitation, humidity, and wind. The ultraviolet correlation exhibits a delay of about 7 days, providing a meteorological measure of the incubation period. Our work reveals a seasonality of COVID‐19 and a high risk of a pandemic resurgence in winter, implying a need for seasonal adaption in public policies.