Was school closure effective in mitigating coronavirus disease 2019 (COVID-19)? Time series analysis using Bayesian inference

OBJECTIVES: The Coronavirus disease 2019 (COVID-19) pandemic is causing significant damage to many nations. For mitigating its risk, Japan called on all elementary, junior high, and high schools nationwide to close beginning March 1, 2020. However, its effectiveness in decreasing the disease burden has not been investigated. METHODS: We used daily data of the COVID-19 and coronavirus infection incidence in Japan until March 31, 2020. Time-series analyses were conducted using the Bayesian method. Local linear trend models with interventional effects were constructed for the number of newly reported cases of COVID-19, including asymptomatic infections. We considered that the effects of the intervention started to appear nine days after the school closure. RESULTS: The intervention of school closure did not appear to decrease the incidence of coronavirus infection. If the effectiveness of school closure began on March 9, the mean coefficient α for the effectiveness of the measure was calculated to be 0.08 (95% confidence interval −0.36 to 0.65), and the actual reported cases were more than predicted, yet with a rather wide confidence interval. Sensitivity analyses using different dates also did not demonstrate the effectiveness of the school closure. DISCUSSION: School closure carried out in Japan did not show any mitigating effect on the transmission of novel coronavirus infection.