This 900-person delta cluster in Mass. has CDC freaked out—74% are vaccinated

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CDC estimates 35K symptomatic infections in US per week among 162 million vaccinated.

Enlarge / Foot traffic along Commercial Street in Provincetown, Mass., on July 20, 2021. Provincetown officials have issued a new mask-wearing advisory for indoors, regardless of vaccination status, on the latest data showing that Provincetown COVID cases are increasing.

An analysis of a COVID-19 cluster of around 900 people in Massachusetts—74 percent of whom are vaccinated—is among the alarming data that spurred the Centers for Disease Control and Prevention to reverse course on masks this week.

According to an internal CDC document first obtained by The Washington Post Thursday evening, data on the Provincetown, Massachusetts, cluster showed that vaccinated people carried surprisingly high levels of the delta coronavirus in their noses and throats. In a study of a subset of people in the cluster, published at 1pm ET Friday by the CDC, Massachusetts health officials reported that fully vaccinated infected people appeared to have similar viral loads as unvaccinated infected people. More importantly, vaccinated people were found to be spreading the dangerous virus variant to other vaccinated people.

The CDC-published study included 469 cases from the cluster, 346 of which were in fully vaccinated people. Of those breakthrough infections, 79 percent had symptoms, with cough, headache, sore throat, myalgia, and fever being the most common symptoms. There were five hospitalizations in the subset: one in an unvaccinated person with underlying medical conditions and four in fully vaccinated people, two of whom had underlying medical conditions. No deaths from cases linked to the cluster have been reported to date.

Nationwide, the CDC estimated that there are 35,000 symptomatic breakthrough infections per week among 162 million fully vaccinated Americans.

The internal CDC document overall highlights that delta is extremely contagious—much more so than previous versions of the virus, as well as the common cold or even the seasonal flu. Delta is more in line with the contagiousness of chickenpox, the CDC document said.

US officials should acknowledge that with delta dominating the country, “the war has changed,” the document read. Officials who spoke with the Post say that the analyses and the urgency the document contains are what prompted the CDC to reverse its masking guidance earlier this week. The CDC now recommends indoor masking, regardless of vaccination status, in schools, in areas with “high” or “substantial” COVID-19 transmission, or when there’s contact with vulnerable people, such as unvaccinated children or immunocompromised people.

But the document shared with the Post two days after the CDC mask update goes further, saying, “Given higher transmissibility and current vaccine coverage, universal masking is essential to reduce transmission of the delta variant.”

The document also focused on the needle that the CDC must now thread with its unpopular health messaging—emphasizing the critical need for everyone to be vaccinated, while also acknowledging the perhaps not-so-rare risk of breakthrough infections and the need to keep up mitigation efforts even after vaccination. Despite the concerning data on delta, vaccines have still proven to be highly effective against severe disease, hospitalization, and death. They remain the most powerful tool to end the health crisis and reclaim some version of normality. But there are clearly caveats, and the CDC has yet to publicly release all the data it has to back up its new alarm over delta.

In May, CDC officials abruptly told people that once they were fully vaccinated, they could rip off their masks in most settings, even in crowded, indoor ones. The rhetoric around the change highlighted the effectiveness of vaccines and suggested the guidance was crafted as an incentive for vaccination—dangling freedom from masks as a reward for getting your shots. But vaccines were never 100 percent effective and many health experts were critical of the abruptness of the move and the fact that it wasn’t carried out in stages or phases, linked to transmission levels or vaccination rates, for instance. Some also noted that, without clear metrics for issuing and retracting health measures, it would be difficult to go back on masking if a game changer—such as delta—arose.

This post has been updated to include new data from the study published by the CDC Friday.

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