Assessing the effectiveness of mandatory outdoor mask policy: The natural experiment of Campania

: Face masks are possibly the main symbol of the COVID-19 pandemic. Once rarely used in Western countries, in the last two years they have become an object it is impossible to leave one's home without. Italy made their use a legal requirement, even outdoors, from late 2020 to early 2022. The effectiveness of this policy in reducing COVID-19 cases has been widely debated. The recent cancellation of their mandatory use in Italy offers an interesting setting in which to test its impact, since one Italian region (Campania) extended the restriction for a further three weeks. We aim to shed some light on the real-world impact of mandatory use of face masks outdoors, identifying the effect of this policy on the spread of COVID-19. By means of a quantitative analysis, employing a synthetic control method approach, we find that Campania had statistically the same number of cases as its synthetic counterfactual, built from a donor pool formed from the other Italian provinces. Hence, results suggest that while it imposes a burden on the public, the use of face masks outdoors is not correlated with a decrease in the number of COVID-19 cases.