Vaccinated people can carry COVID-19 virus, CDC report shows.
Agency’s study of COVID-19 breakthrough infections bolsters research about transmissibility of the coronavirus
A new analysis of a massive Massachusetts COVID-19 outbreak offers alarming new insights on so-called “breakthrough” infections.
This hasn’t changed: Unvaccinated people continue to be the major drivers of the nation’s pandemic, according to the U.S. Centers for Disease Control and Prevention.
But the new research, referenced by CDC Director Dr. Rochelle Walensky on Tuesday and detailed in the CDC’s Morbidity and Mortality Weekly Report on Friday, bolsters the theory that vaccinated people can become infected and spread the more transmissible delta variant.
Based on this cluster, the CDC has recommended that everyone, including the fully vaccinated, should wear masks in indoor public settings in areas with significant COVID-19 transmission.
Here’s what the CDC reported.
QWhat
just happened?
A
During July, 469 cases of COVID-19 were reported following multiple summer events and large public gatherings in Provincetown, a seaside town at the northern tip of Cape Cod, Massachusetts.
Q
What were these people doing?
A
They reported attending densely packed indoor and outdoor events at venues that included bars, restaurants, guest houses and rental homes.
Q
Were they vaccinated?
A
Of these cases, about three-quarters (74%) were “breakthrough” infections, occurring in people who were fully vaccinated. About onequarter (26%) occurred in unvaccinated people.
Q
Which vaccines did they get?
A
All three: PfizerBioNTech (46%), Moderna (38%) and Johnson & Johnson (16%). They had been vaccinated, on average, nearly three months before infection.
Q
Is the delta variant involved?
A
Yes. Delta was found in 90% of specimens. QDid they get sick?
A
Overall, 274 (79%) of the vaccinated patients with breakthrough infection had symptoms. The most common symptoms were cough, headache, sore throat, fatigue and fever.
Q
Were the illnesses severe?
A
Five people were hospitalized. Of these, four were fully vaccinated. Their ages ranged from 20 to 70. Two had underlying medical conditions. One patient, in his 50s, was not vaccinated and had multiple underlying medical conditions.
QDid ANo.
anyone die?
Q
Could the vaccinated people with “breakthrough” infections transmit the virus to others?
A
The study didn’t look at that. It did not investigate whether someone got their infection from a vaccinated person. But it did find that the levels of the virus, as estimated by PCR testing, were similar in vaccinated and unvaccinated infections. This strongly suggests that vaccinated people, if they are infected, can transmit the virus just as readily as unvaccinated
people.
Q
Did the vaccinated people who were not infected also have transmissible virus?
A
The study did not look at uninfected people. It only measured viral levels in infected breakthrough cases. But the science seems clear: If the virus isn’t living in your body, you won’t transmit it.
Q
What don’t we yet know?
A
The findings in the CDC report are subject to at least four limitations. First, the data are insufficient to draw any conclusions about the effectiveness of COVID-19 vaccines against the delta variant. Experts have predicted that as vaccination coverage increases, vaccinated persons will likely represent a larger proportion of new COVID-19 cases.
Secondly, it might have missed some cases. If you don’t have any symptoms, you’re unlikely to be tested. So the true number of “breakthroughs” might be higher.
Third, we don’t know if the people in Provincetown are representative of the general population. The events primarily attracted men, not women. There may have been other differences, such as age or underlying health conditions, that put them at greater or lesser risk of infection.
Finally, PCR tests aren’t a perfect measure of viral load and potential transmissibility. Microbiological studies are required to confirm these findings.