CDC study on breakthrough COVID-19 cases indicates age is the biggest factor

Who Had Covid-19 Vaccine Breakthrough Cases? Data shows the vaccines kept working through the Delta surge, though some groups were at higher risk of breakthrough infections or death. The New York Times

After a summer of reports of breakthrough coronavirus infections, when it seemed that everyone knew someone who tested positive after vaccination, recently released federal data sheds light on how common these cases really were, how severe they became and who was most at risk.

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Compared with the unvaccinated, fully vaccinated people overall had a much lower chance of testing positive for the virus or dying from it, even through the summer’s Delta surge and the relaxation of pandemic restrictions in many parts of the country. But the data indicates that immunity against infection may be slowly waning for vaccinated people, even as the vaccines continue to be strongly protective against severe illness and death.

“The No. 1 take-home message is that these vaccines are still working,” said Dr. David Dowdy, an epidemiologist at the Johns Hopkins Bloomberg School of Public Health. “If you saw these data for any disease other than Covid, what everyone’s eyes would be drawn to is the difference between the unvaccinated and fully vaccinated lines.”

The data shows notable differences in breakthrough death rates by age and slight differences in both case and death rates by vaccine brand, trends that experts say are important to consider as tens of millions of Americans weigh whether to get a booster shot.

The data, from the Centers for Disease Control and Prevention, is based on health department records from 14 states and two cities. A second dashboard reveals similar trends for hospitalized patients with and without vaccination.

All vaccinated age groups saw similar rates of breakthrough infection, and they all had much lower rates of infection and death compared with their unvaccinated peers.

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While every age group had similar rates of breakthrough cases, death rates varied more drastically by age. Unvaccinated seniors were the most likely to die from Covid of any group. Still, vaccinated people 80 and older had higher death rates than unvaccinated people under 50.

“Age is our top risk factor for vaccine breakthrough deaths,” said Theresa Sokol, the state epidemiologist in Louisiana, one of the jurisdictions that contributed to the C.D.C. data.

Breakthrough deaths among seniors may be because of immunosenescence, or the weakening of the immune system in older people, said Heather Scobie, an epidemiologist at the C.D.C. who helps lead the team that produced the new data.

“They don’t usually form as robust a response to vaccination,” added Dr. Scobie. “Hopefully the booster dose for ages 65 years and older will address that issue.”