A new study by the U.S. Centers for Disease Control and Prevention showed that three-quarters of individuals who became infected with COVID-19 at public events in a Massachusetts county had been fully vaccinated.
The CDC study found vaccinated individuals had a similar amount of virus presence as the unvaccinated, suggesting that, unlike with other variants, vaccinated people infected with the Delta variant could transmit the virus, the CDC said.
CDC Director Rochelle Walensky said this was a “pivotal discovery” leading to CDC’s recommendation this week that masks be worn in areas where cases were surging as a precaution against possible transmission by fully vaccinated people.
“The masking recommendation was updated to ensure the vaccinated public would not unknowingly transmit virus to others, including their unvaccinated or immunocompromised loved ones,” Walensky said.
The CDC said 469 cases were found among Massachusetts residents from July 3 to 26 related to the Cape Code outbreak. Of those, 74% were among fully vaccinated people. The CDC said its study excluded residents of 22 other states. Barnstable County reported that as of July 30, 934 total cases had been associated with the outbreak.
The CDC said that overall, 79% of the vaccinated individuals who were infected with COVID-19 also reported symptoms such as cough, headache, sore throat and fever. Four had to be hospitalized, the CDC said.
Vaccinated individuals had received one of the three available shots made by Pfizer Inc and BioNTech , Moderna Inc or Johnson & Johnson, the data showed.
The study’s authors recommended local health authorities consider requiring masks in indoor public settings regardless of vaccination status or the number of cases in the community.
The CDC said that people with COVID-19 reported having been at densely packed indoor and outdoor events including bars, restaurants, guest houses and rental homes.
— Reporting by Manas Mishra in Bengaluru