Kansas counties with mask mandates had half the rate of new infections

A new study by economists at the University of Kansas has found that counties in the state where residents are obliged to wear masks in public have seen about half as many new coronavirus infections as counties that do not have a mask mandate in force.

The study by the university’s Institute for Policy & Social Research is part of a countrywide trend, experts said. Localities that impose mask mandates often see fewer cases, fewer hospitalizations, fewer deaths or lower test-positivity rates than nearby localities that do not.

The same trend has been seen in Alabama, Kansas, Oklahoma, South Carolina and Texas, according to a report from Prevent Pandemics, a nonprofit group advocating pandemic-fighting measures.

“Mask mandates, if they are done well, can increase mask use — and increased mask use is part of an effective response,” said Dr. Thomas R. Frieden, a former director of the Centers for Disease Control and Prevention who now runs Resolve to Save Lives, of which Prevent Pandemics is a part.

The Kansas study began after Gov. Laura Kelly issued a statewide mask order on July 2, but allowed counties to opt out of it. She was obliged to give counties that freedom under a law passed in June limiting her emergency management powers. All but 24 of the state’s 105 counties formally opted out of her mask order, and only 20 counties enforced it.

“Economists love natural experiments, and Kansas was running a natural experiment,” said Donna K. Ginther, director of the university’s Institute for Policy & Social Research, which conducted the study.

Differences in the spread of the virus between the masked and unmasked counties began to appear about two weeks later, she said, “and in mid-August, cases really began to take off.”

In the mask-wearing counties, new-case rates stayed roughly steady at about 7 per 100,000 residents through mid-October, her figures show, while they doubled in counties without mandates, to about 14 per 100,000.

Cellphone-tracking data from the University of Maryland showed no differences in how often people left home in the counties with or without mask mandates, she said, so it seemed likely that the masks made the difference.

The study data has been presented to state officials, but has not yet been submitted to an academic journal for review, Dr. Ginther said.

On Monday, Dr. Scott Gottlieb, a former commissioner of the Food and Drug Administration, published an editorial in The Wall Street Journal recommending a limited and temporary nationwide mandate for wearing masks as the best way to stop the spread of the coronavirus as winter approaches. Dr. Anthony S. Fauci, the nation’s top infectious disease expert, said on Friday that the country should consider taking such actions.