How Easily Can Vaccinated People Spread COVID?

The fear of breakthrough COVID-19 infections spoiled the summer. In the early days of vaccine bliss, many Americans had thought that the shots were a ticket to normalcy—and at least for a while, that’s precisely what public-health experts were telling us: Sure, it was still possible for vaccinated people to get COVID-19, but you wouldn’t have to worry much about spreading it to anyone else. Interim guidance shared by the CDC in March stated that these cases “likely pose little risk of transmission,” and a few weeks later, CDC Director Rochelle Walensky said that “vaccinated people do not carry the virus.”

And then came Delta. The hyper-contagious variant sent cases skyrocketing and led ICUs to yet again fill up with COVID patients. And it also spurred a full-on freak-out that our understanding of who could spread the virus was all wrong. In early August, on a huge cluster of COVID cases in Provincetown, Massachusetts, concluding that 74 percent of cases had occurred in vaccinated people. The supposed implication of that finding was even more ominous: Vaccinated people were to spread the virus as the unvaccinated. The CDC quickly went back to recommending that vaccinated people wear masks indoors while news outlets ran headlines such as “.” The worst-case scenario—that vaccinated people might be going about their lives only to be seeding tons of new coronavirus cases—all of a sudden seemed possible.