By CBSBoston.com Staff

BOSTON (CBS) – Centers for Disease Control Director Rochelle Walensky confirmed Friday that the agency relied on data from the Provincetown COVID cluster to update its national guidance earlier this week for fully vaccinated people to start wearing masks again in some indoor settings.

Data from the cluster on the Cape, which is now up to 882 cases, showed the amount of the Delta coronavirus variant in samples collected from vaccinated and unvaccinated cases were virtually identical.

“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,” Walensky said in a statement.  “This finding is concerning and was a pivotal discovery leading to CDC’s updated mask recommendation.”

The Delta variant of the coronavirus spreading across the country is just as contagious as chickenpox, according to an internal CDC document confirmed by CBS News. Researchers also reportedly found the variant is more transmissible than MERS, SARS, Ebola, the common cold and smallpox.

The CDC document, first revealed by the Washington Post, was part of a presentation of unpublished data on Thursday that shows fully vaccinated people might spread the Delta variant at the same rate as unvaccinated people.

According to CBS, slides from Thursday’s presentation recommend the CDC publicly “acknowledge the war has changed,” warning that “breakthrough infections may be as transmissible as unvaccinated cases” with the Delta variant.

The revelation came more than two days after the CDC announced that fully vaccinated Americans in communities with substantial or high COVID transmission should once again wear face masks in public indoor settings.

Massachusetts COVID-19 hot spots (WBZ-TV)

According to a map of COVID tracking data on the CDC’s website, Suffolk County, Bristol County, Cape Cod and Nantucket are among the Massachusetts areas with substantial or high transmission.

On Friday, the state’s Department of Public Health updated its guidance, recommending that some fully vaccinated people in Massachusetts wear face masks indoors.

CBSBoston.com Staff