Centers for Disease Control and Prevention published new data indicating that nearly three-fourths of people infected in a Massachusetts Covid-19 outbreak were fully vaccinated against the coronavirus with four of them ending up in the hospital.
The new data, published in the U.S. agency’s Morbidity and Mortality Weekly Report, also found that fully vaccinated people who get infected carry as much of the virus in their nose as unvaccinated people, and could spread it to other individuals.
“This finding is concerning and was a pivotal discovery leading to CDC’s updated mask recommendation,” CDC Director Dr. Rochelle Walensky said in a statement. “The masking recommendation was updated to ensure the vaccinated public would not unknowingly transmit virus to others, including their unvaccinated or immunocompromised loved ones.”
While the delta variant continues to hit unvaccinated people the hardest, some vaccinated people could be carrying higher levels of the virus than previously understood and are potentially transmitting it to others, Walensky told reporters on a call Tuesday. She added the variant behaves “uniquely differently from past strains of the virus.”
The data published Friday was based on 469 cases of Covid associated with multiple summer events and large public gatherings held in July in Barnstable County, Massachusetts, which encompasses Cape Cod and is just outside Martha’s Vineyard. The events were held in Provincetown, according to NBC News. Approximately three-quarters, or 74%, of the cases occurred in fully vaccinated people who had completed a two-dose course of the mRNA vaccines or received a single shot of Johnson & Johnson’s.
Overall, 274 vaccinated patients with a breakthrough infection were symptomatic, according to the CDC. The most common side effects were cough, headache, sore throat, muscle pain and fever. Among five Covid patients who were hospitalized, four were fully vaccinated, according to the agency.
No deaths were reported.