Effectiveness of public health and social measures during the early COVID-19 waves in Japan

Abstract

State of emergency and other mobility-restricting public health and social measures were used during the COVID-19 pandemic in Japan. This study aimed to epidemiologically estimate their impact on the pandemic by comparing observed and counterfactual situations in Osaka and Tokyo during 2020–2021. Weekly nighttime population data were used to predict the effective reproduction number. The first three epidemic waves in 2020–2021 were modelled using the age-dependent transmission model. We used the nighttime population data in 2019 as the counterfactual, and simulated the COVID-19 epidemic in the absence of public health and social measures. In Osaka, predicted counterfactual mortality was 71525 deaths in the first wave, 13589 in the second, and 18814 in the third. These estimates were approximately 832, 100, and 21 times the observed values, respectively. In Tokyo, the predicted counterfactual mortality was 57018, 4361, and 17100 deaths for the three waves, respectively. These estimates were approximately 416, 42, and 14 times the observed numbers, respectively. If the nighttime population remained comparable to that in 2019 and if it continued to predict the epidemic in the absence of public health and social measures, we could have seen far more COVID-19 deaths in Osaka and Tokyo.