Why vaccines don’t work as well in older people

Senior shots

As flu season returns, I’ve been thinking about the annual shot ritual. My parents used to be first in line to get me my slate of vaccines when I was a child. But now, it seems like they’re barely aware of the routine shots they need to get as older adults.

In the 2024-2025 flu season, 48% of US adults age 65 and older were vaccinated for the flu, well below the 70%  goal of the US Department of Health and Human Services. William Schaffner, a professor of medicine and infectious disease expert at the Vanderbilt University School of Medicine, attributes that gap to misinformation. Older adults grew up at a time where vaccines were mainly aimed at children, and they aren’t always aware that there specific inoculation recommendations for seniors.

But they still need to keep up with their shots. Older patients’ immune systems have a harder time fighting off infections, Schaffner explains, and they’re more likely to have medical conditions like diabetes or heart disease that make it more likely for an infection to become serious.

That’s why certain shots for seniors, like the flu vaccine, contain adjuvants that boost immune responses, or have a higher dose, “designed to particularly help a somewhat diminished immune system in older people,” Schaffner says.

Yet vaccines can actually be less effective for older people. A new study from researchers at Allen Institute in Seattle recently investigated the reason why.

By using RNA sequencing technology to compare the immune systems of older adults against younger adults, the researchers found that T cells – the crux of the immune system’s protective response – lose some of their functions as we age. This can make some vaccines, like the flu shot, less effective in older adults.

Given these results, researchers are closer to making all types of vaccines tailored specifically for certain age groups, says Claire Gustafson, an experimental immunologist at the Allen Institute and one of the paper’s authors.

But Gustafson wants to make it clear that it’s important for people to get the current shots. “Vaccines are effective,” she said. “They’re still good. We just have identified ways that they can be better.” — Annika Inampudi

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