Data-driven estimation of change points reveals correlation between face mask use and accelerated curtailing of the COVID-19 epidemic in Italy

Italy was the first Western country to be seriously affected by COVID-19, and the first to implement drastic measures, which have successfully curtailed the epidemic. To understand which containment measures altered disease dynamics, we estimate change points in COVID-19 dynamics from official Italian data. We find excellent correlation between nationwide lockdown and the epidemic peak in late March 2020. Surprisingly, we find a change point in mid April, which does not correspond to national measures, but may be explained by regional interventions. Change points in regional COVID-19 dynamics correlate well with local distribution of free face masks and regional orders requiring their mandatory use. Regions with no specific interventions showed no change point during April. We speculate that widespread use of face masks and other protective means has contributed substantially to keeping the number of new Italian COVID-19 cases under control in spite of society turning towards a new normality.