CDC Links Mask Advice to ‘Compelling’ Real-World Shot Study


The Pfizer Inc.-BioNTech SE vaccine and the Moderna Inc. shot were 94% effective against symptomatic Covid-19 in a real-world study of health-care workers that was key to the federal decision to ease restrictions for fully vaccinated people.

“This report provided the most compelling information to date that Covid-19 vaccines were performing as expected in the real world,” Rochelle Walensky, head of the U.S. Centers for Disease Control and Prevention, said in a statement. “This study, added to the many studies that preceded it, was pivotal to CDC changing its recommendations for those who are fully vaccinated against Covid-19.”

The research found that symptomatic illness was cut by 94% among the health-care personnel who were fully vaccinated, according to a report Friday by the CDC. It was reduced by 82% among those who were partially vaccinated. The analysis used data from health-care workers at 33 sites across 25 states from January to March.

Full vaccination was defined in the study as seven or more days after the second dose. Partial vaccination was measured as 14 days after the first dose through six days after the second dose.

The report adds to growing evidence on the real-world effectiveness of messenger-RNA vaccines. It follows by a day the CDC’s decision to relax its guidelines with a recommendation that vaccinated people can go maskless indoors, and end social distancing protocols.

The findings in the study also support the CDC’s recommendation for people to take both doses of the vaccine to get the most protection, according to the agency. Nearly half of Americans have now had at least one vaccine dose, according to the Bloomberg Vaccine Tracker, with 35.8% fully vaccinated.

The agency still recommends vaccinated people wear masks while flying on planes, riding public transportation, visiting certain congregate settings and where required by state and local governments or businesses.

Despite the CDC’s shift, some states and businesses have indicated they will make their own judgments about whether and when to modify mask protocols. Pfizer said it would maintain its masking and social-distancing guidance for employees regardless of vaccination status, in part to protect workers with compromised immune systems.

Moderna said it would continue to abide by mask-wearing guidelines in Massachusetts, where the biotechnology company is based. Governor Charlie Baker said Massachusetts will update its reopening plans next week.

©2021 Bloomberg L.P.

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