Pattern of COVID-19 epidemics in Japan influenced by the control measures

BackgroundCOVID-19 has spread worldwide since it appeared in 2019. In contrast to many other countries with epidemics, Japan differed in that it avoided lockdowns and instead asked people for self-restraint. A travel campaign was conducted with a huge budget, but the number of PCR tests is severely limited. These choices may have influenced the course of the epidemic. MethodsThe increase or decrease in the classes of SARS-CoV-2 variants was estimated by analyzing the published sequences with an objective multivariate analysis. This methodology does not rely on unverifiable assumptions. It observes the samples in multiple directions, digesting complex differences into simpler forms. The results were compared over time with the number of confirmed cases, PCR tests, and overseas visitors. ResultsThree epidemic peaks in Japan have been caused by domestically mutated variants. However, due to the relaxation of immigration restrictions, several infective variants have been imported from abroad and are currently competing for expansion. In other countries, there are few other cases where multiple variants have peaked. The chaotic situation in Japan will continue for a while, in part, because no effort has been made to find asymptomatic carriers and details of the vaccination program are undecided.