The impact of mask-wearing and shelter-in-place on COVID-19 outbreaks in the United States

Zhang, Kevin; Vilches, Thomas N.; Tariq, Mehreen; Galvani, Alison P.; Moghadas, Seyed M.

Objectives A hasty reopening has led to a resurgence of COVID-19 in the United States (US). We sought to quantify the impact of several public health measures, including non-medical mask-wearing, shelter-in-place, and detection of silent infections to help inform COVID-19 mitigation strategies. Methods We expanded a previously established agent-based disease transmission model and parameterized it with estimates of COVID-19 characteristics and US population demographics. We implemented non-medical mask-wearing, shelter-in-place, and case isolation as control measures and quantified their impact on reducing the attack rate and adverse clinical outcomes. Results We found that non-medical mask-wearing by 75% of the population reduced infections, hospitalizations, and deaths by 37.7% (IQR: 36.1% - 39.4%), 44.2% (IQR: 42.9% - 45.8%), and 47.2% (IQR: 45.5% - 48.7%), respectively, in the absence of a shelter-in-place strategy. Sheltering individuals aged 50 to 64 was the most efficient strategy, decreasing attack rate, hospitalizations, and deaths by over 82% when combined with mask-wearing. Under simulated scenarios, outbreak control can be achieved, bringing the attack rate to below 1%, if at least 33% of silent pre-symptomatic and asymptomatic infections are identified and isolated. Conclusions Mask-wearing, even with the use of non-medical masks with only 20% efficacy in preventing disease transmission, has a substantial impact on outbreak control. Shelter-in-place strategies remain an important public health intervention, amid ongoing outbreaks.