The impact of temperature on the transmission potential and virulence of COVID-19 in Tokyo, Japan

ABSTRACT Background Assessing the impact of temperature on COVID-19 epidemiology is critical for implementing non-pharmaceutical interventions. However, few studies have accounted for the nature of contagious diseases, i.e., their dependent happenings. Aim We aimed to quantify the impact of temperature on the transmissibility and virulence of COVID-19 in Tokyo, Japan. We employed two epidemiological measurements of transmissibility and severity: the effective reproduction number ( R t ) and case fatality risk (CFR). Methods We used empirical surveillance data and meteorological data in Tokyo to estimate the R t and time-delay adjusted CFR and to subsequently assess the nonlinear and delay effect of temperature on R t and time-delay adjusted CFR. Results For R t at low temperatures, the cumulative relative risk (RR) at first temperature percentile (3.3°C) was 1.3 (95% confidence interval (CI): 1.1-1.7). As for the virulence to humans, moderate cold temperatures were associated with higher CFR, and CFR also increased as the temperature rose. The cumulative RR at the 10 th and 99 th percentiles of temperature (5.8°C and 30.8°C) for CFR were 3.5 (95%CI: 1.3-10) and 6.4 (95%CI: 4.1-10.1). Conclusions This study provided information on the effects of temperature on the COVID-19 epidemiology using R t and time-delay adjusted CFR. Our results suggest the importance to take precautions to avoid infection in both cold and warm seasons to avoid severe cases of COVID-19. The results and proposed framework will also help in assessing possible seasonal course of COVID-19 in the future.