Assessing Public Health and Social Measures Against COVID-19 in Japan From March to June 2021

BackgroundPublic health and social measures (PHSM) against COVID-19 in Japan involve requesting the public to voluntarily reduce social contact; these measures are not legally binding. The effectiveness of such PHSM has been questioned with emergence of the SARS-CoV-2 Alpha variant (B.1.1.7), which exhibited elevated transmissibility. Materials and MethodsWe investigated the epidemic dynamics during the fourth epidemic wave in Japan from March to June 2021 involving pre-emergency measures and declaration of a state of emergency (SoE). We estimated the effective reproduction number (R-t) before and after these interventions, and then analyzed the relationship between lower R-t values and each PHSM. ResultsWith implementation of pre-emergency measures (PEM) in 16 prefectures, the R-t was estimated to be < 1 in six prefectures; its average relative reduction ranged from 2 to 19%. During the SoE, 8 of 10 prefectures had an estimated R-t < 1, and the average relative reduction was 26%-39%. No single intervention was identified that uniquely resulted in an R-t value < 1. ConclusionAn SoE can substantially reduce the R-t and may be required to curb a surge in cases caused by future SARS-CoV-2 variants of concern with elevated transmissibility. More customized interventions did not reduce the R-t value to < 1 in this study, but that may be partly attributable to the greater transmissibility of the Alpha variant.