Fact check: CDC study links mask mandates to slowing COVID-19 infections and deaths
The claim: CDC study found that face masks have a negligible effect on the spread of COVID-19
A new study from the Centers for Disease Control and Prevention found a link between face mask mandates and a reduction in COVID-19 cases and deaths, but at least one widely shared report wrongly interprets that data.
One America News Network on March 7 published an article under the headline “CDC: Face masks don’t prevent COVID-19, study finds masks have negligible impact on coronavirus numbers.” The post claims “the CDC has admitted face masks do little to prevent the spread of COVID-19 amid mounting pressure to lift mask mandates across the U.S.”
However, the CDC’s study doesn’t say that. In fact, it doesn’t study mask efficacy at all. Instead, it links mask mandates to “statistically significant decreases in county-level daily COVID-19 case and death growth rates within 20 days of implementation.”
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“Over the course of the pandemic, the scientific evidence and our understanding of masks have grown. The data we now have conclusively show that widespread use of masks is a very effective way to reduce the spread of COVID-19,” CDC spokeswoman Jasmine Reed wrote in an email to USA TODAY.
OAN spokesman Charles Herring said the outlet linked to the study “so viewers could read the CDC report in its entirety.”
What exactly was the CDC studying?
Reed said the CDC’s report “did not examine the effectiveness of masks.”
Instead, it analyzed the connection between mask mandate policies and the rate of new county-level COVID-19 cases and deaths. It also examined the link between allowing on-site restaurant dining and the number of coronavirus cases and deaths.
The study used county-level data from March 1 through Dec. 31 of last year, comparing data from before mandates went into effect to the time period when they were in place.
While it controlled for other policies that have been used to try to mitigate new infections from COVID-19 — including bar closures, stay-at-home orders and bans on gatherings of 10 or more people — it did not account for some others, such as physical distancing recommendations and other types of business closures.
The study also did not measure compliance with and enforcement of mask mandates and prohibitions on dining at restaurants.
“What they’re looking at here is efficacy of mask mandates. They’re not looking at masks in and of themselves,” Josh Petrie, research professor in the University of Michigan’s School of Public Health, told USA TODAY. “They don’t know how well people complied with these mandates or what proportion of the pop was actually wearing masks.”
“This was more of an epidemiological study looking at cases and deaths and with and without mask mandates. That’s what this study was pursuing to try to answer,” said Michael Bisesi, vice dean and interim chair of environmental health sciences in Ohio State University’s College of Public Health.
What did the study find?
The authors found that the growth rate of new COVID-19 cases and deaths dropped after mask mandates were put in place.
In the first 20 days after implementing mask mandates, new cases slowed by 0.5 percentage points. They continued to fall over the 100 days analyzed in the study. COVID-19 death rates dropped by 0.7 percentage points in the first 20 days after masks were required.
Decreases in the rate of new infections and deaths from the virus were statistically significant, the study’s authors found.
“Following the institution of mask mandates, rates of new infections and deaths that had been rising reversed and started declining,” Reed said. “Immediately after these mandates were instituted, these declines were statistically significant.”
The study also found a statistically significant increase in the rate of COVID-19 infections and deaths starting 40 days after indoor or outdoor dining at restaurants was allowed.
OAN zeroed in on a portion of the report that outlines the slowing rate of infections and deaths after mask mandates were put in place. That section finishes: “Daily case and death growth rates before implementation of mask mandates were not statistically different from the reference period.”
But the “reference period” is defined by the report as the 20 days before mask mandates started. That period is used as the benchmark against which researchers compared days 21 through 60 before mask mandates were adopted, and the 100 days after.
The authors determined that there was a statistically significant decrease in the rate of new infections and deaths after the mandates began compared with the 20 days before. But the difference between the 20 days prior to the mask mandate starting and the 40 days before that period was not statistically significant.
Herring dismissed those results, claiming unnamed experts told OAN the reductions in spread the study found were not significant.
Experts interviewed by USA TODAY said OAN had “misinterpreted” or “mischaracterized” the findings of the CDC study.
“Their perspective on the study and results to me are contrary to what was stated in the actual study itself,” Bisesi said. “…I just don’t know based on reading the OAN summary how they came to the same conclusions because the CDC conclusions were favorable.”
Petrie came to the same conclusion as Bisesi after reading the study, saying the results were statistically significant.
What do other studies say about mask mandates?
The CDC’s report is the latest in a growing body of evidence establishing mask mandates as an effective strategy in curbing the virus.
Data released by the agency in November looking at COVID-19 incidence in Kansas following a statewide mask mandate also found the measure resulted in a cut back of infectious cases. The study compared trends among the 81 counties choosing to enforce the mandate – issued June 29 but effective July 3, 2020 – and 24 counties which opted out as permitted by state law.
Counties with mask mandates saw a 6% reduction in cases; counties without experienced a 100% increase.
While the downtrend could also have been due to other countermeasures like social distancing, Kansas’ findings mirror observations from other states and countries.
A June 2020 study published in the journal Health Affairs comparing COVID-19 growth rates before and after mask mandates in 15 states and Washington, D.C., found mask wearing led to a reduction in daily cases, especially over time.
Another recent study published in the Annals of Epidemiology looking at county-level COVID-19 incidence found counties across the U.S. with shorter lockdowns, none at all or without statewide mask mandates when the state reopened were more likely to see a sharp spike in infectious cases during the summer months (the study looked at over 3,000 counties between June 1 and Sept. 30).
And in the German city of Jena, first in the country to implement public mask wearing last April, masks led to a 75% decrease in new COVID-19 cases in little under three weeks, one December study found.
Fact check: Masks and vaccines are effective at combating COVID-19 spread
Our rating: False
The claim that a CDC study found face masks to have a negligible effect on the spread of COVID-19 is FALSE. The study referenced in the OAN report says the opposite, noting that mask mandates were linked to “statistically significant decreases” in COVID-19 case within 20 days of implementation.
Our fact-check sources:
- U.S. Centers for Disease Control and Prevention, March 5, “Association of State-Issued Mask Mandates and Allowing On-Premises Restaurant Dining with County-Level COVID-19 Case and Death Growth Rates — United States, March 1–December 31, 2020”
- U.S. Centers for Disease Control and Prevention, Nov. 27, 2020, “Trends in County-Level COVID-19 Incidence in Counties With and Without a Mask Mandate — Kansas, June 1–August 23, 2020”
- Kansas.gov, June 29, 2020, “Governor Laura Kelly Announces Masks Must be Worn Statewide”
- Annals of Epidemiology, Feb. 14, “Differences in rapid increases in county-level COVID-19 incidence by implementation of statewide closures and mask mandates — United States, June 1–September 30, 2020”
- Health Affairs, June 16 2020, “Community Use Of Face Masks And COVID-19: Evidence From A Natural Experiment Of State Mandates In The US”
- France24, April 24, 2020, “Germany to oblige mandatory face masks from Monday”
- Proceedings of the National Academy of Science of the United States of America, Dec. 3, 2020, “Face masks considerably reduce COVID-19 cases in Germany”
- U.S. Centers for Disease Control and Prevention, Feb. 12, “Decline in COVID-19 Hospitalization Growth Rates Associated with Statewide Mask Mandates — 10 States, March–October 2020”