An initial set of interventions, including the closure of host and hostess clubs and voluntary limitation of non-household contact, probably greatly contributed to reducing the disease incidence of coronavirus disease (COVID-19) in Japan, but this approach must eventually be replaced by a more sustainable strategy. To characterize such a possible exit strategy from the restrictive guidelines, we quantified the next-generation matrix, accounting for high- and low-risk transmission settings. This matrix was used to project the future incidence in Tokyo and Osaka after the state of emergency is lifted, presenting multiple ‘post-emergency’ scenarios with different levels of restriction. The effective reproduction numbers ( R ) for the increasing phase, the transition phase and the state-of-emergency phase in the first wave of the disease were estimated as 1.78 (95% credible interval (CrI): 1.73–1.82), 0.74 (95% CrI: 0.71–0.78) and 0.63 (95% CrI: 0.61–0.65), respectively, in Tokyo and as 1.58 (95% CrI: 1.51–1.64), 1.20 (95% CrI: 1.15–1.25) and 0.48 (95% CrI: 0.44–0.51), respectively, in Osaka. Projections showed that a 50% decrease in the high-risk transmission is required to keep R less than 1 in both locations—a level necessary to maintain control of the epidemic and minimize the risk of resurgence.
【저자키워드】 COVID-19, Japan, projection, countermeasure, Exit strategy, next-generation matrix, 【초록키워드】 coronavirus disease, risk, Transmission, Reproduction number, incidence, First wave, Contact, Tokyo, club, Host, approach, effective, Transition phase, decrease, the epidemic, initial, was used, the disease, required, less, reducing, maintain, replaced, contributed, presenting, quantified, lifted, 【제목키워드】 Intervention, second wave,