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No Debate: New Study Shows How Masks Slow Spread of COVID-19

June 17, 2020

Some people fight it, but you can’t beat a mask for preventing the spread of COVID-19 in public when social distancing isn’t possible.

Here’s some evidence: A study released this week in Health Affairs, a peer-reviewed healthcare journal, found that masks prevented as many as 230,000 to 450,000 COVID-19 cases by May 22 in the 15 states, including Connecticut, and the District of Columbia that adopted mask mandates early in the pandemic. The fast-track version of the study, “Community Use Of Face Masks And COVID-19: Evidence From A Natural Experiment Of State Mandates In The United States,” appeared  in the journal June 16 ahead of the final, accepted version.

The study evaluated public data sets and all state orders between April 1 and May 21. Gov. Ned Lamont’s executive order required Connecticut residents to wear a protective mask in public effective April 20.

“The study,” the researchers concluded, “provides evidence that states in the U.S. mandating use of face masks in public had a greater decline in daily COVID-19 growth rates after issuing these mandates compared to states that did not issue mandates.”

Using a statistical method called an event study, the researchers found a reduction in COVID-19 spread by examining daily changes in county-level COVID-19 growth rates in the 15 states and District of Columbia.

Here are the reductions they found, in percentage points, during the days immediately after the executive orders:

  • 1-5 days: 0.9 percentage points.
  • 6-10 days: 1.1 percentage points.
  • 11-15 days: 1.4 percentage points.
  • 16-20 days: 1.7 percentage points.
  • 21-or-more days: 2.0 percentage points.

The estimates, the researchers said, are significant because they represent in the same period up to 19 percent of the effects of other social-distancing measures, such as shelter-in-place orders and closures of schools, restaurants, bars and entertainment venues. Yet they said the number of potential cases averted, up to 450,000, should be viewed cautiously because there was no way to measure compliance with, or enforcement of, the mask mandate in each state.

But it doesn’t change the advice of health professionals since the onset of COVID-19.

“It’s as important as ever to wash your hands, wear a mask and don’t touch your face,” says Keith Grant, APRN, head of infectious disease for Hartford HealthCare. “Those are still the basic ways to avoid COVID-19 infection.”

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