State COVID Mask-Wearing Mandates Work: CDC

Yet more data supporting the efficacy of wearing masks to help slow the spread of coronavirus disease 2019 (COVID-19), and more ammunition for those arguing that wearing masks should be mandated. Infection Control Today® recently looked at the stark differences in Kansas between counties that decided to mandate mask wearing and those that didn’t. Kansan counties that did not mandate the wearing of masks had much higher incidents of infection and hospitalization due to COVID-19.

A study in Morbidity and Mortality Weekly Report (MMWR), published by the Centers for Disease Control and Prevention (CDC), expands the scope of the mask mandate examination, with CDC investigators comparing COVID-19 hospitalization rates in 10 states before and after those states issued mandates that residents must wear a mask when outside their home, and also that masks must be worn by workers in retail businesses and restaurants.

Data were collected from March 1 to October 17, 2020 via COVID-NET, a surveillance system that tracks COVID hospitalizations. A “site” is defined as a group of counties within a state that participates in COVID-NET.

“The association between mask mandates and COVID-19–associated hospitalization growth rates was measured using a time-based categorical variable with four mutually exclusive categories based on the week (Sunday through Saturday), with the effective date of the mask mandate (‘implementation week’) characterized as follows: ≥4 weeks before the implementation week; <4 weeks before the implementation week (reference); <3 weeks after the implementation week; and ≥3 weeks after the implementation week,” the study states.

Hospitalizations for COVID-19 dropped by a statistically significant 5.5 percentage points for adults from 18 to 64, compared to the hospitalization rates in the 4 weeks preceding the implementation of the mask mandates. For people 40- to 64-years old, mask mandates resulted in a 2.9 percentage point reduction in hospitalizations for COVID-19 3 weeks or less after the mask mandate, but this age group also saw a 5.5 percentage-point decline in hospitalizations at 3 weeks or more. Hospitalization rates for adults over 65 also declined 3 weeks after the mask mandate, though those declines were not statistically significant, the study states. But the lesser decline in the oldest age group may have been because people that age were more inclined to wear a mask in the first place.

“Masks are intended to reduce emission of virus-laden respiratory droplets, which is especially relevant for persons who are infected with SARS-CoV-2 but are asymptomatic or presymptomatic; masks also help reduce inhalation of respiratory droplets by the wearer,” the study states. It adds that “the declines in hospitalization growth rates <3 weeks after the implementation week are consistent with the incubation period of SARS-CoV-2; in a report based on an analysis of publicly reported confirmed COVID-19 cases, the median estimated incubation period was 5.1 days, and most symptomatic patients reported symptoms within 11.5 days after exposure.”

Mask wearing should be part of a multipronged application of infection prevention methods (or the Swiss cheese approach to infection prevention featured on the ICT® website) that prevent the transmission of SARS-CoV-2. The investigators conclude that “wearing a mask reduces exposure, transmission, and strain on the health care system with likely direct effects on COVID-19 morbidity and associated mortality.”