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| - A recent study from China suggests that high temperature and ultraviolet (UV) radiation cannot decrease the epidemics of Coronavirus disease 2019 (Covid-19). To determine whether COVID-19 incidence is modulated by meteorological factors, meta-regression of Japanese prefectural data was herein conducted. We extracted 1) cumulative numbers of confirmed Covid-19 patients in each Japanese prefecture from January to April 2020; 2) populations per 1-km2 inhabitable area in each prefecture in 2020; and 3) meteorological factors at each prefectural capital city from January to April 2020. Meteorological factors included monthly mean air temperature (degree Celsius), wind speed (m/s), sea level air pressure (hPa), relative humidity (%), and percentage of possible sunshine (%); monthly total of sunshine duration (h) and precipitation (mm); and monthly mean daily maximum ultraviolet (UV) index. To adjust for prefectural population density, we defined the incidence of Covid-19 as the cumulative number of Covid-19 patients divided by the population per 100-km2 inhabitable area. Random-effects meta-regression was performed, and its graph depicted Covid-19 incidence (plotted as the logarithm transformed incidence on the y-axis) as a function of a given meteorological factor (plotted on the x-axis). A slope of the meta-regression line was significantly negative as a function of the mean air temperature (coefficient, -0.127; P = 0.023), the mean sea level air pressure (coefficient, -0.351; P < 0.001), and the mean daily maximum UV index (coefficient, -0.001; P = 0.012) which indicated that Covid-19 incidence decreased significantly as air temperature, air pressure, and UV increased. In conclusion, higher air temperature, air pressure, and UV may be associated with less Covid-19 incidence.
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