- A CDC study of a COVID outbreak suggests vaccinated people may spread the Delta variant as easily as the unvaccinated.
- Almost all the symptomatic vaccinated people in the study had mild symptoms like headaches and sore throats.
- The study was a major factor in the CDC’s new mask guidance for vaccinated people.
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The Centers for Disease Control and Prevention released a study on Friday which suggests that fully vaccinated people can transmit the Delta variant of the coronavirus just as easily as the unvaccinated – a find that may change the calculus of what’s safe for vaccinated people to do, now that the Delta variant is responsible for more than 80% of US cases.
“Unlike with other variants, vaccinated people infected with Delta can transmit the virus,” CDC Director Rochelle Walensky said in a statement released alongside the new report.
The study is a big part of the reason why the CDC changed its guidance for vaccinated people on Tuesday, saying that where COVID-19 transmission is substantial or high, vaccinated people should mask up again indoors in public.
Delta was responsible for at least 90% of the cases in this outbreak, according to viral sequencing. It didn’t matter much which shots vaccinated people with Delta infections got, but the most common symptoms – including cough, headache, and sore throat – were mild.
Massachusetts is a state with a relatively high vaccination rate
The study, released by the CDC on Friday, followed an outbreak that started in Barnstable County, an area of coastal Massachusetts that’s popular for summer vacations and parties, and attracts people from across the US.
According to the report, during the first half of July, multiple large events were held in an unnamed town there (local media coverage makes clear that it’s Provincetown). The festivities included “densely packed indoor and outdoor events at venues that included bars, restaurants, guest houses, and rental homes.”
The outbreak is noteworthy, as Massachusetts is a state with a relatively high vaccination rate.
Among Massachusetts residents tied to the cluster and tracked by the state health department, 74% of the cases (346 infections) were in fully vaccinated people. The vast majority of the vaccinated infections were among men, with a median age of 42.
But the outbreak extends far beyond Massachusetts, with the total number of cases tied to the outbreak now estimated at more than 830 people, Provincetown Town Manager Alex Morse said on Facebook.
Though the study demonstrates that vaccinated people are at greater risk of infection with Delta, the overwhelming majority of the breakthrough cases in the cluster have been mild, with symptoms including coughs, headaches, sore throats, muscle aches, and fevers.
At least four vaccinated people were hospitalized, ranging from ages 20 to 70, but no deaths were reported. Two of the hospitalized patients had underlying conditions.
In other words, the vaccines are still achieving what they were designed to do: prevent severe infections and deaths.
Delta will ‘find any gap in our defenses’
Experts have been saying for weeks now that the Delta variant spreads both faster and more easily than other versions of the coronavirus, but this study provides some of the first clear evidence for why that’s the case.
Not only is the viral load of a person infected with Delta estimated to be about 1,000 times higher than with other versions of the virus, this study shows that a vaccinated person’s load is roughly equal to an unvaccinated person’s, meaning that vaccinated and unvaccinated people likely spread Delta equally well.
Andy Slavitt, a former senior adviser to President Joe Biden’s coronavirus response team, has called Delta “COVID on steroids,” while a leaked CDC slide presentation obtained by the Washington Post late Thursday said “the war has changed,” now that Delta is here.
The CDC slides also say Delta is more contagious than the common cold – on par with chickenpox in its ability to spread.
“What the Delta variant will do is that it will find any gap in our defenses,” Hilary Babcock, medical director of infection prevention at Barnes-Jewish Hospital and St. Louis Children’s Hospital in Missouri previously told Insider.
“You have to be really more careful about it all the time.”