In the United States, counties in states with mask-wearing mandates saw their growth in Covid-19 case and death rates slow last year, but growth rates increased in counties where states allowed on-site restaurant dining, according to a CDC Morbidity and Mortality Weekly Report (MMWR) released Friday.

CDC report finds mask mandates linked to a decrease in Covid-19 case and death growth rates

For the study, researchers examined the association between mask mandates, indoor or outdoor restaurant dining, and Covid-19 cases and deaths between March 1, 2020 and Dec. 31, 2020. To do so, the researchers analyzed county-level data on mask mandates, restaurant closures, and changes in Covid-19 case and death growth rates relative to the date when the restrictions were implemented.

The researchers designed their models to control for mask mandates, restaurant and bar closures, stay-at-home orders, and gathering bans. However, the researchers identified at least three limitations to their study: Their models did not control for other factors that might affect case and death rates, including physical distancing recommendations; their analysis did not measure enforcement or compliance with these policies; and their analysis did not differentiate between indoor and outdoor dining, ventilation adequacy, and adherence to physical distancing and occupancy requirements.

Overall, the researchers found the growth rate of Covid-19 cases and deaths declined in counties mandating mask wearing but increased in counties allowing restaurants to open for dining on their premises.

The researchers found 2,313—or 73.6%—of the country's 3,142 counties had state-issued mask mandates from March 1, 2020 to Dec. 31, 2020. Within 20 days of counties implementing the mask mandates, county-level data showed a decrease in daily Covid-19 case and death growth rates, the researchers found.

Specifically, the researchers found mask mandates were associated with a half percentage point decrease in the daily Covid-19 case growth rate one to 20 days after implementation and a 1.8 percentage point decrease 81 to 100 days after implementation. The researchers also found mask mandates were associated with a 0.7 percentage point decrease in the daily Covid-19 death growth rate one to 20 days after implementation and a 1.9 percentage point decrease 81 to 100 days after implementation.

In comparison, the researchers found 3,076—or 97.9%—of U.S. counties allowed restaurants to reopen for on-premises dinning. Within 41 to 60 days of restaurants reopening, county-level data showed an increase in daily Covid-19 case and death growth rates, the researchers found.

In particular, the researchers found allowing on-premises dining at restaurants was associated with a 0.9 percentage point increase in the daily case growth rate 41 to 60 days after reopening and a 1.1 percentage point increase 81 to 100 days after reopening. The researchers also found allowing on-premises dining at restaurants was associated with a 2.2 percentage point increase in the daily death growth rate 61 to 80 days after reopening and 3 percentage point increase 81 to 100 days after reopening.

Ultimately, the researchers concluded, "State mask mandates and prohibiting on-premises dining at restaurants help limit potential exposure to SARS-CoV-2, reducing community transmission of Covid-19."

The report came as many state and local officials have begun lifting restrictions intended to slow the coronavirus's transmission, citing America's accelerating Covid-19 vaccine rollout and recent declines in newly reported coronavirus cases, deaths, and hospitalizations.

Good? Bad? Ugly? We've updated our take on what's next for the epidemic.

Public health officials urge states to not loosen coronavirus restrictions

But public health officials and experts say America is currently at a crossroads in its coronavirus epidemic, with the potential to see continued progress or for that progress to reverse if Americans stop adhering to public health measures intended to curb the virus's spread. For example, Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases and chief medical adviser for the White House's Covid-19 response, and CDC Director Rochelle Walensky have urged state and local officials to not ease coronavirus-related restrictions and warned that that loosening restrictions prematurely could result in a fourth surge in America's coronavirus epidemic.

"We've just now recently experienced the worst surge," Fauci said Friday during a White House coronavirus briefing, noting that the Unite States has plateaued at between 60,000 and 70,000 newly reported coronavirus cases per day, which "invariably means that [the country is] at risk for another spike."

Separately, Walensky on Friday said, "You have decreases in cases and deaths when you wear masks, and you have increases in cases and deaths when you have in-person restaurant dining. And so we would advocate for policies, certainly while we're at this plateau of a high number of cases, that would listen to that public health science."

Where America's coronavirus epidemic stands

Overall, data compiled by the Times shows that U.S. officials on Sunday reported about 40,336 new cases of the novel coronavirus. As of Monday morning, officials had reported about 29 million cases since the United States' epidemic began.

According to the Times, the United States' average daily number of newly reported coronavirus cases over the past week was 58,745—down by 12% compared with the average from two weeks ago.

However, the Times' data showed that, as of Monday morning, the rates of newly reported coronavirus cases were "staying high" in Washington, D.C., and 16 states that have reported a daily average of at least 15 newly reported cases per 100,000 people over the past week. Those states are Alaska, Arizona, Colorado, Connecticut, Delaware, Florida, Massachusetts, Michigan, New Jersey, New York, Pennsylvania, Rhode Island, South Dakota, Tennessee, Texas, and Vermont.

In addition, the rate of newly reported coronavirus cases was "going up" as of Monday morning in Maine, Nebraska, and the U.S. Virgin Islands, which have had comparatively lower case rates, the Times reports.

According to the data, rates of newly reported coronavirus cases were "staying low" or declining from previously higher rates in the remaining U.S. states and territories.

Meanwhile, data from The Atlantic's COVID Tracking Project shows there were 40,212 Americans with Covid-19 hospitalized for treatment on Sunday, including 8,137 who were receiving care in an ICU and 2,801 who were on a ventilator.

Further, data from the Times shows that U.S. officials reported about 682 new deaths linked to the coronavirus on Sunday. As of Monday morning, officials had reported about 524,652 U.S. deaths linked to the virus since the country's epidemic began.

(Rabin, New York Times, 3/5; Associated Press/NBC News, 3/6; McNamara, Medscape, 3/5; Howard, CNN, 3/5; CDC MMWR, 3/5; Soucheray, CIDRAP News, 3/5; DePasquale/Grullón Paz, New York Times, 3/6; Budryk, The Hill, 3/7; Duster, CNN, 3/7; New York Times, 3/8; "COVID Tracking Project," The Atlantic, accessed 3/8).