The agency’s new masking guidelines for vaccinated people, introduced on Tuesday, were based on the information presented in the document. The C.D.C. recommended that vaccinated people wear masks indoors in public settings in communities with high transmission of the virus.
But the internal document hints that even that recommendation may not go far enough. “Given higher transmissibility and current vaccine coverage, universal masking is essential,” the document said.
The agency’s data suggest that people with weak immune systems should wear masks even in places that do not have high transmission of the virus. So should vaccinated Americans who are in contact with young children, older adults, or otherwise vulnerable people.
There are roughly 35,000 symptomatic infections per week among 162 million vaccinated Americans, according to data collected by the C.D.C. as of July 24 that was cited in the internal presentation. But the agency does not track all mild or asymptomatic infections, so the actual incidence may be higher.
Infection with the Delta variant produces virus amounts in the airways that are tenfold higher than what is seen in people infected with the Alpha variant, which is also highly contagious, the document noted.
The amount of virus in a person infected with Delta is a thousandfold more than what is seen in people infected with the original version of the virus, according to one recent study.
The C.D.C. document relies on data from multiple studies, including an analysis of a recent outbreak in Provincetown, Mass., which began after the town’s Fourth of July festivities. By Thursday, that cluster had grown to 882 cases. About 74 percent were vaccinated, local health officials have said.
Article source: https://www.nytimes.com/2021/07/30/health/covid-cdc-delta-masks.html