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

Background: Italy was the first Western country to be seriously affected by COVID-19, and the first to implement drastic measures, which successfully curtailed the first wave of the epidemic.
Methods: To understand which containment measures altered disease dynamics, we estimated change points in COVID-19 dynamics from official Italian data.
Results: We found an excellent correlation between nationwide lockdown and the epidemic peak in late March 2020. Surprisingly, we found a change point in mid-April, which did not correspond to national measures, but may be explained by regional interventions. Change points in regional COVID-19 dynamics correlated 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.
Conclusions: Our findings of the observed correlation between face mask use and disease dynamics lend further support to the importance of face masks in addition to lockdowns and other restrictions for the control of COVID-19.