Face Masks, Public Policies and Slowing the Spread of COVID-19 : Evidence from Canada

We estimate the impact of mask mandates and other non-pharmaceutical interventions (NPI) on COVID-19 case growth in Canada, including regulations on businesses and gatherings, school closures, travel and self-isolation, and long-term care homes. We partially account for behavioural responses using Google mobility data. Our identification strategy exploits variation in the timing of indoor face mask mandates staggered over two months in the 34 public health districts in Ontario, Canada's most populous province. We find that mask mandates are associated with a 25 percent or larger weekly reduction in new COVID-19 cases in July and August, relative to the trend in absence of mask mandate. Additional analysis with province-level data provides corroborating evidence. Counterfactual policy simulations suggest that mandating indoor masks nationwide in early July could have reduced the number of new cases in Canada by 25 to 40 percent in mid-August, which corresponds to 700 to 1,100 fewer cases per week