The Centers for Disease Control and Prevention released a study Friday finding that vaccinated people diagnosed with COVID-19 in a Massachusetts town had nearly the same amount of virus in their bodies as unvaccinated patients. The majority of cases in an outbreak were found to be among the vaccinated.
The findings were the basis for the new federal guidance this week for indoor mask-wearing and the warnings that even fully inoculated people can be contagious.
Still, the authors included major caveats in the study, most notably that it only included subjects who happened to get tested, a limitation that could bias the results. The outbreak also took place in a setting that is not representative of the country as a whole — the beach town Provincetown, Massachusetts, a popular gay destination, during a major summer party event. Thousands of attendees gathered in densely packed crowds both indoors and outdoors, making person-to-person transmission more likely.