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Why Older Adults Are More at Risk for Severe Breakthrough Infections

Catching a serious case of COVID is rare if you’re vaccinated, but older adults bear the burden  

Older woman in the hospital with COVID, wearing a face mask.

RUBEN BONILLA GONZALO / Getty Images

En español | The coronavirus vaccines held their ground during the delta variant’s dominance, and health officials are expecting them to keep people from getting sick during omicron’s rein. The latest data show that unvaccinated individuals are roughly 10 times more likely to get COVID-19 than vaccinated and boosted people, Centers for Disease Control and Prevention (CDC) Director Rochelle Walensky has said — and they’re about 20 times more likely to die from it.

Still, because no vaccine is 100-percent effective, breakthrough infections do occur. And on the rare occasion that a vaccinated person falls seriously ill with COVID-19, it’s most often an older adult. Earlier this fall, federal data showed that about 70 percent of breakthrough infections that required hospitalization were among adults 65 and older. This population also accounted for 87 percent of breakthrough deaths. 

study published Dec. 3 in The Lancet Microbe mirrors the CDC’s earlier findings: The majority of patients hospitalized with severe breakthrough cases at the Yale New Haven Health System from early August to mid-October were older, with an average age of about 71.5, researchers found. What’s more, hospital data tracked by the Kaiser Family Foundation (KFF) found that more than two-thirds (69 percent) of breakthrough COVID-19 hospitalizations from June to September occurred among people ages 65 and older, despite this population having the highest vaccination rates.

Chronic diseases, delta and dwindling immunity are likely to blame  

Throughout the pandemic, older adults have been more likely to suffer from COVID complications than their younger peers, and experts say the same reasons that made them more susceptible from the get-go could be causing them to bear the burden of these uncommon severe breakthrough cases, although research is ongoing.

Take, for example, underlying health conditions, which affect about 80 percent of older Americans. Many chronic diseases put people at greater risk for a serious case of COVID-19, and emerging research shows these illnesses can still be a disadvantage even after vaccination.  KFF’s analysis on breakthrough cases, published on Dec. 15, found that larger shares of fully vaccinated adults hospitalized with COVID-19 had chronic conditions like hypertension, diabetes, heart failure and lung disease, compared to patients hospitalized with COVID-19 who were not fully vaccinated.

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.

Who is at highest risk?

large study published in the British Medical Journal identified populations in the U.K. at greatest risk for hospitalization or death from COVID-19, post-vaccination. They include:

  • Individuals who are immunosuppressed from chemotherapy, a recent bone marrow transplant or solid organ transplant, or HIV/AIDS
  • People with neurological disorders, including dementia and Parkinson’s
  • Nursing home residents
  • People with chronic conditions, including Down’s syndrome, kidney disease, sickle cell disease and liver cirrhosis

Source: BMJ

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.


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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.