The effect of a strict facial-mask policy on the spread of COVID-19 in Switzerland during the early phase of the pandemic

During several weeks in the second half of the year 2020, the cantons of Switzerland could choose to adopt the government-determined facial-mask policy, corresponding to mandatory facial-mask wearing on public transport, or a strict facial-mask policy, corresponding to mandatory facial-mask wearing on public transport and in all public or shared spaces where social distancing was not possible. We estimate the effect of introducing the strict facial-mask policy on the spread of COVID-19 in Switzerland during this first phase of the pandemic in 2020, using the cantonal heterogeneity in facial-mask policies. We adjust for social distancing behavior, weather, other non-pharmaceutical policies and further variables. We estimate a significant reduction in the expected spread of COVID-19 in the early pandemic if the strict facial-mask policy is adopted.