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On July 27th, the CDC recommended that fully vaccinated people wear masks indoors in areas with high COVID transmission. What metrics should vaccinated people use to decide when to wear their masks?

This article was published on
July 28, 2021

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SciLine reaches out to our network of scientific experts and poses commonly asked questions about newsworthy topics. Reporters can use these responses in news stories, with attribution to the expert.

SciLine reaches out to our network of scientific experts and poses commonly asked questions about newsworthy topics. Reporters can use these responses in news stories, with attribution to the expert.

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Expert Comments: 

Dave O’Connor, PhD

Since we don’t know ahead of time which areas have high COVID-19 transmission, it is best to err on the side of caution and wear masks whenever you are indoors if you are concerned about being infected with—or transmitting—COVID-19 to others. Those who spend time around those who are unvaccinated, or those who are vaccinated but potentially at high risk, like people who are immunocompromised, should be especially cautious.

Deborah Fuller, PhD

Fully vaccinated people should wear masks in any indoor setting where there are large groups of people whose vaccination status is unknown. Put on a mask when entering a grocery store, a crowded bar or restaurant, when using public transportation, or when attending an indoor event where staying greater than six feet apart is not possible. Those are potential areas of high transmission. Also, before travel, check the CDC website to see if where you’re going has a high COVID-19 infection rate. In those areas, always wear mask unless you’re outdoors or indoors with family and friends whom you know are all vaccinated. Regardless of region, always wear a mask when you enter any health care or senior care facility.

Monica Gandhi, MD, MPH

When the CDC put in their mask guidance on May 13 that the vaccinated need not mask indoors, they were being consistent with the data that vaccines were very effective and reduced transmission.  However, the Delta variant is much more transmissible, leading to more mild breakthroughs among the vaccinated in areas of high community transmission and high cases and hospitalizations among unvaccinated adults. The reason for the increased mild breakthroughs is likely due to higher circulating virus making even vaccinated people likely to be exposed.  Therefore, the CDC has changed to a more metric-based set of mask guidance, rather than a single set of guidelines for the country, in response to a new variant with increased transmissibility. If one lives in an area with high rates of circulating virus (substantial or high transmission), the CDC is recommending that even vaccinated people should mask indoors, which I think is prudent until the Delta wave subsides.

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