6 studies behind the CDC's decision to ease indoor mask guidance

The CDC's May 13 announcement that masks are no longer required in most indoor settings for fully vaccinated Americans was backed by "numerous reports in the literature that demonstrate the safety and real-world effectiveness of the authorized vaccines," according to Rochelle Walensky, MD, the agency's director. 

Here are six studies that supported the CDC's updated mask guidance, as referenced by Dr. Walensky: 

 Vaccine effectiveness in real-world settings

1. Among 6,710 healthcare workers in Israel, Pfizer-BioNTech's vaccine demonstrated 97 percent effectiveness at protecting against symptomatic infection, and 86 percent effectiveness against asymptomatic infection, according to a study published May 6 in the Journal of the American Medical Association. 

2. In a U.S.-based study involving nearly 4,000 healthcare workers, Pfizer and Moderna's mRNA vaccines were 90 percent effective at preventing any COVID-19 infection. The research was published April 2 in the CDC's Morbidity and Mortality Weekly Report

3. A separate MMWR report from the CDC found mRNA vaccines were 94 percent effective at preventing COVID-19-related hospitalizations among adults aged 65 and older. 

Protection against variants 

4. Pfizer's vaccine demonstrated 89.5 percent effectiveness against the B.1.1.7 variant, first detected in the U.K., which became the dominant U.S. strain in April, according to a May 5 study published in The New England Journal of Medicine. The vaccine was also 75 percent effective against the B.1.351 variant, which first emerged in South Africa, the findings showed. 

"Additional studies confirm that the Moderna and Johnson & Johnson vaccines are also effective against circulating variants," Dr. Walensky added. 


5. Among those who experienced a rare case of reinfection after getting vaccinated, the subsequent infection was more likely to have a lower viral load, indicating decreased transmissibility, according to research published March 29 in Nature Medicine. 

6. An April 21 MMWR report from the CDC found no facility-associated secondary transmission among vaccinated nursing home residents.


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