Why Older Adults Are More at Risk for Severe Breakthrough Infections

Another explanation for the disparity: Older adults have a less robust immune system than younger people, and the protection afforded by the vaccines may wane faster for them because of it, says Mark K. Slifka, an expert in vaccine development and the longevity of vaccine-induced immune responses at Oregon Health & Science University.

Add to the mix the facts that Americans 65 and older were first in line to get their shots last year, says Jill Foster, M.D., a pediatric infectious disease physician at the University of Minnesota Medical School, and that it’s not unusual for vaccines to fall from their peak efficacy as time goes on. Plus, the highly contagious delta variant, which still accounts for roughly 40 percent of new COVID cases, “is just different enough from the virus that the vaccine was developed for that you also need to have super-extra-high amounts of antibodies to fight it,” Foster adds.

A September CDC report found that overall the vaccines were 86 percent effective at preventing hospitalization from COVID-19 during delta’s summer surge; among adults 75-plus, that number dropped to 76 percent. This gap helps explain why health officials first recommended booster shots for older adults ahead of younger populations

Researchers are still studying how the vaccines will hold up against the omicron variant, but early evidence suggests the shots are less protective against the new strain. For this reason, all fully vaccinated adults are now encouraged to get a booster to rev up the immune response; 16- and 17-year-olds who were vaccinated with two doses of Pfizer’s product are also eligible..

‘It continues to be a time to be cautious’

Given that older adults are more likely to experience these severe breakthrough cases than younger populations, practicing a few extra precautions doesn’t hurt, experts say —  especially with new COVID cases, hospitalizations and deaths climbing once again.

For example, infectious disease expert William Schaffner, M.D., a professor at Vanderbilt University School of Medicine — who is fully vaccinated but says, “I have gray hair myself” — runs errands early in the morning when crowds are less dense and avoids large group events indoors. He also wears a mask in indoor public settings, which the CDC recommends regardless of vaccination status.

Being older and having a chronic health condition — such as heart disease, lung disease, diabetes or obesity — “those things stack the cards a little bit in favor of you getting severe disease, should you become infected,” Schaffner says. "It continues to be a time to be cautious.”

The key, Slifka says, is to be mindful of your own health conditions when making plans — whether that’s a trip to the grocery store or a gathering with friends — because everybody’s risk is going to look a little bit different. And if you have questions about where you stand on that spectrum, “it's a good time to just have that conversation with your doctor,” Slifka says.

Maintaining some sense of flexibility is also important, notes Hyung Chun, M.D., a cardiologist and associate professor at Yale School of Medicine, who coauthored the Lancet study on breakthrough infections. “It's such a fluid situation. We're still in the process of really finding out about COVID itself, as well as the efficacy of vaccines and other treatments,” he says. Meaning the safeguards recommended today could look a little different a few months down the road, depending on the science and the situation.  

Finally, if you are not vaccinated, “get your vaccine as quickly as possible,” Schaffner says, since doing so will significantly decrease your odds of getting sick with COVID-19. And a booster shot, when you’re eligible, will provide even more protection. The vaccines will also help prevent future breakthrough cases from happening to others. “The more people who are vaccinated, that will diminish the circulation of the virus, and the virus will have fewer chances to create both serious and milder infections,” Schaffner says.

Editor's Note: This story, originally published Sept. 14, 2021, has been updated to reflect new information.

Rachel Nania writes about health care and health policy for AARP. Previously she was a reporter and editor for WTOP Radio in Washington, D.C. A recipient of a Gracie Award and a regional Edward R. Murrow Award, she also participated in a dementia fellowship with the National Press Foundation.