A new JAMA Insights Clinical Update from the CDC's COVID-19 response team discusses the association of changes in COVID-19 case rates and death rates with implementation of state-issued mask mandates and allowance of any on-premises restaurant dining.

As Guy, et al. (2021) explain, "Evidence-based prevention strategies can reduce the transmission of SARS-CoV-2, the virus that causes COVID-19. Consistent and correct use of masks can prevent SARS-CoV-2 transmission, which predominantly occurs through inhalation and other exposure to respiratory droplets from infected persons. Mask use is particularly important because pre-symptomatic and asymptomatic spread is responsible for nearly 60% of COVID-19 cases. Universal and proper masking results in substantial community benefits. To better leverage the prevention benefit of masks on community transmission, many states require that people wear a mask in public. As of March 1, 2021, 36 states and the District of Columbia had a mask mandate in effect."

The researchers continue, "Indoor venues such as restaurants, where physical distancing (≥6 ft) is difficult to maintain and consistent use of masks is not possible, can increase the risk of transmission. Between March and April 2020, 49 states and the District of Columbia prohibited on-premises dining at restaurants. However, by mid-June 2020, on-premises dining was allowed by all states and the District of Columbia. As of March 1, 2021, all states allow on-premises restaurant dining. In a recent report, the CDC evaluated the association between state-issued mask mandates and allowing any on-premises restaurant dining and COVID-19 cases and deaths between March 1 and Dec. 31, 2020. State-issued mask mandates were associated with decreases in daily COVID-19 case growth rates and death growth rates within 20 days of implementation, ranging from 0.5 percentage points to 1.9 percentage points. Meanwhile, allowing on-premises restaurant dining was associated with increases in daily COVID-19 case growth rates 41 to 100 days after implementation and increases in daily death growth rates 61 to 100 days after implementation, ranging from 0.9 percentage points to 3.0 percentage points. Because the percentage point decreases (for mask mandates) and increases (for on-premises dining) refer to changes in daily growth rates, changes over time amplify exponentially and these measures could result in averting a substantial number of COVID-19 cases and deaths. An earlier study that examined mask mandates in 15 states and the District of Columbia between April 8 and May 15, 2020, estimated that reductions in daily case growth rates of the same magnitude were associated with more than 200 000 COVID-19 cases averted. However, these investigations did not consider mask use and SARS-CoV-2 transmission in other indoor venues such as bars."

The researchers point out that "Although closing restaurants for on-premises dining can limit potential exposure to SARS-CoV-2, such orders could also have an adverse influence on the economy, the food services industry, and food service industry employees. Restaurants can continue to operate by limiting food service to drive-through, delivery, takeout, and curbside pickup to reduce the risk of COVID-19 spread. For restaurants that continue to provide on-premises dining, several strategies can reduce risk of exposure for employees and customers and thus slow community COVID-19 spread. Such strategies include having staff stay home when appropriate, requiring mask use, providing adequate ventilation or outdoor dining, promoting frequent hand hygiene and cleaning, and making modifications that promote physical distancing."

Reference: Guy GP, et al. Mask Mandates, On-Premises Dining, and COVID-19. JAMA. Published online April 1, 2021. doi:10.1001/jama.2021.5455