A new study by the US Centers for Disease Control and Prevention (CDC) found that the Delta variant produced similar amounts of virus in vaccinated and unvaccinated people if they get infected.
The study, published in CDC’s weekly report, focused on 469 COVID-19 cases identified among Massachusetts residents who had traveled to Barnstable County, a summer vacation destination, from July 3 to 17.
According to the study, a total of 346 cases, about 74 percent, occurred in fully vaccinated people. Testing identified the Delta variant in 90 percent of specimens from 133 patients.
“Cycle threshold values were similar among specimens from patients who were fully vaccinated and those who were not. Among persons with breakthrough infection, four (1.2 percent) were hospitalized, and no deaths were reported,” the report added.
The study demonstrated that Delta infection resulted in similarly high SARS-COV-2 viral loads in vaccinated and unvaccinated people. “High viral loads suggest an increased risk of transmission and raised concern that, unlike with other variants, vaccinated people infected with Delta can transmit the virus,” said CDC Director Ms. Rochelle Walensky.
The new finding is concerning and was a pivotal discovery leading to CDC’s updated mask recommendation, urging vaccinated Americans to resume wearing masks in schools and in public indoor spaces in COVID-19 hot spots across the country.
“The masking recommendation was updated to ensure the vaccinated public would not unknowingly transmit the virus to others, including their unvaccinated or immunocompromised loved ones,” Ms. Rochelle said.
Further, the CDC suggested jurisdictions to consider expanded prevention strategies, like universal masking in indoor public settings, particularly for large public gatherings that include travelers from many areas with differing levels of SARS-COV-2 transmission.