By Carolyn Johnson et al.
A sobering scientific analysis published Friday found that three-quarters of the people infected during an explosive coronavirus outbreak fueled by the delta variant were fully vaccinated. The report on the Massachusetts cases, from the Centers for Disease Control and Prevention, offers key evidence bolstering the hypothesis that vaccinated people can spread the more transmissible variant and may be a factor in the summer surge of infections.
The data, detailed in the CDC’s Morbidity and Mortality Weekly Report, helped persuade agency scientists to reverse recommendations on mask-wearing and advise that vaccinated individuals wear masks in indoor public settings in some circumstances.
Critically, the study found that vaccinated individuals carried as much virus in their noses as unvaccinated individuals, strongly suggesting that vaccinated people could spread the virus to others. The CDC was criticized this week for changing its mask guidance without publishing the data it relied on. The report released Friday contains some of that data.