Preliminary evaluation of voluntary event cancellation as a countermeasure against the COVID-19 outbreak in Japan as of 11 March, 2020

Background: To control COVID−19 outbreak in Japan, sports and entertainment events were canceled in Japan for two weeks from 26 February to 11 March. It has been designated as voluntary event cancellation (VEC). Object: This study predicts the effectiveness of VEC enduring and after its implementation. Method: We applied a simple susceptible−infected−recovery model to data of patients with symptoms in Japan during 14 January to VEC introduction and after VEC introduction to 8 March. We adjusted the reporting delay in the latest few days. Results: Results suggest that the basic reproduction number, R0, before VEC introduced as 2.50 with a 95% confidence interval (CI) was [2.43, 2.55] and the effective reproduction number, Rv, after VEC introduced as 1. 88; its 95% CI was [1.68,2.02]. Discussion and Conclusion: Results demonstrated that VEC can reduce COVID−19 infectiousness by 35%, but R0 remains higher than one.