ST. LOUIS — Mask mandates in St. Louis and St. Louis County quickly and drastically slowed coronavirus infection rates this summer compared with outlying counties, according to a new study from St. Louis University.
But effects of the mask orders were also durable, the study says: After 12 weeks, the average daily growth rate of coronavirus cases in the two urban counties was still 40% lower than in counties without the policy. Moreover, the mandates reduced “the unequal burden” on higher-risk groups, decreasing transmission rates in more densely populated areas and on racial minorities, who have been disproportionately infected, the research says.
“It was something that was fast and effective,” said Enbal Shacham, lead author of the study, and a professor at St. Louis University’s College for Public Health and Social Justice. “And that’s exactly what we need right now.”
The research reinforces the public health benefits of mask-wearing even as medical leaders — including one of the study’s authors, Dr. Alex Garza — are imploring Missouri Gov. Mike Parson to order a statewide mask mandate and limit gatherings, dining and shopping. As hospitalizations soar, health officials warn of an imminent crisis across Missouri.
“We are past the time when individual behavior alone can address this disaster,” Garza, chief of the St. Louis Metropolitan Pandemic Task Force, said in a press briefing on Friday. “The spread of cases are blanketing the state and no locale is safe anymore.”
I have great respect for our Governor, I know him to be a caring person. I too appreciate local control. But we are now under uniform threat, like war, it requires a coordinated response. We each give to protect others, we buy time for the vaccine. “The wolf is at the door.” pic.twitter.com/BGtP5nJfHi— Steve Edwards (@SDECoxHealth) November 15, 2020
Parson has resolutely rejected mandates, instead deferring to local officials and urging residents to take “personal responsibility.” His office did not respond to questions from the Post-Dispatch on Tuesday.
Shacham said that the White House Coronavirus Task Force advised Missouri to adopt a statewide mask mandate back in August. At the time, dozens of the state’s counties were designated in the “red zone” for high virus transmission, and the overwhelming majority of them did not, and do not, have a mask mandate.
The latest data from the task force, which represents the region’s large health care systems, showed that St. Louis and St. Louis County have lower per-capita rates of virus-related admissions than other Missouri counties in the metropolitan area.
Shacham’s study began in early July, when St. Louis Mayor Lyda Krewson and St. Louis County Executive Sam Page first ordered residents to wear masks in public.
She and her co-authors — SLU professors Stephen Scroggins and Matthew Ellis, plus Garza, an SSM Health executive — compared the average daily increase in COVID-19 caseloads in St. Louis and St. Louis County with that in neighboring Jefferson, Franklin and St. Charles counties, which do not have mask mandates.
In the three weeks before the mandates, both sets of jurisdictions had been seeing similar growth rates for their respective caseloads.
But in the weeks after the mandates, researchers noted a remarkable slowdown in caseload growth in masked-up counties. To illustrate the decrease, they highlighted comparisons at two different intervals: three weeks after the local mask mandates went into place, then 12 weeks after.
After three weeks, average daily case growth in St. Louis and St. Louis County was 44% less than that of the outlying counties. And after 12 weeks, that reduction changed only slightly, to 40%.
The study also produced a model to estimate the probable growth of virus caseloads in St. Louis and St. Louis County, if neither had a mask mandate. The model accounted for areas with higher population density, higher proportions of nonwhite residents, and lower median household incomes — all factors that correspond with higher rates of infections.
But after St. Louis and St. Louis County adopted mask mandates, “the disparity of infection rate by race and population density was no longer significant,” the study says.
Residents in middle- and high-income communities protected themselves from infection by staying at home, the study’s authors theorized. Minorities and city residents who were more likely to work in “essential” jobs such as grocery stores, health care and public transportation, and couldn’t stay home, were greater beneficiaries of the mask policies.
“The mask policy that was enacted in many communities may have provided a more equal approach to reducing COVID-19 infections, as it occurred in St. Louis,” the authors write.
The virus is now much more widespread. Still, Shacham believes a mask mandate would reduce infections in Missouri by a similar magnitude.
“It’s something tangible,” she said, “that we can do right now.”
Editor's note: The study has been submitted to an academic journal for publication, and is now being peer-reviewed, Shacham said. Results were featured last week on the U.S. Centers for Disease Control and Prevention's weekly science update.