New details on CDC's Provincetown investigation portray delta variant as serious threat

Newly published details of the Provincetown outbreak indicate that the now-dominant delta variant may be able to spread among fully vaccinated people.

Adding more insight into the CDC’s updated mask guidance, newly published details of the Provincetown outbreak raise concern that the now-dominant delta variant may be able to spread among fully vaccinated people. Following multiple large gatherings in Provincetown, Mass., from July 3-17, investigators identified 469 COVID-19 cases, two-thirds of which were in fully vaccinated people. The delta variant was responsible for 90% of those cases. The breakthrough infections were among people vaccinated with Pfizer, Moderna and Johnson & Johnson. None of the vaccinated people died, but most had some symptoms. During the outbreak investigation, researchers learned that the amount of virus in the noses of vaccinated people experiencing a breakthrough infection was the same as in an unvaccinated person -- a worrying sign vaccinated people can spread the virus. "This finding is concerning and was a pivotal discovery leading to CDC’s updated mask recommendation," said CDC Director Rochelle Walensky in a statement.