Flu Shot Facts, Part 1 of 5: Why the Flu Hits Harder After 65

This series breaks down "Flu Shots for Older Adults: What to Know & Do for 2026" by geriatrician Dr. Leslie Kernisan, MD MPH, of Better Health While Aging. The original article and its insights are hers; you can read the full piece here.

"It's that time of the year: fall, which I think of as flu vaccination time." That's how Dr. Leslie Kernisan opens her 2026 guide to flu shots for older adults, and it's a good reminder for every family caring for an aging parent or grandparent.

Over the next five posts, we're walking through the key points of her article in bite-sized pieces. We're starting with the big question: why does the flu deserve extra attention as we age?

What is the flu?

As Dr. Kernisan explains, influenza is a contagious respiratory virus. It commonly causes sore throat, cough, fever, and body aches. For a healthy younger adult, that might mean a miserable week. For an older adult, it can lead to hospitalization or worse.

The numbers behind flu season

Dr. Kernisan cites CDC estimates that each year the flu affects between 9.4 and 51 million Americans, causing roughly 120,000 to 710,000 hospitalizations and 6,300 to 52,000 deaths.

And the most recent season was a hard one. According to her article, the 2025-2026 flu season brought "the highest levels of hospitalization and deaths seen in over ten years.

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Why age makes a difference

Dr. Kernisan notes that older adults' immune systems don't respond as strongly as younger people's do. An aging immune system makes fewer antibodies, which means the body has a harder time fighting off infection, and a harder time building protection from a vaccine. (That's also why there are special flu vaccines for older adults, which we'll cover in Part 2.)

Does the flu shot still work for seniors?

Yes. Per the article, when the vaccine is well matched to the strains going around, it lowers the risk of flu illness by about 40-60% overall. Even though older adults respond less strongly, vaccination still makes a real difference: Dr. Kernisan points to the 2017-2018 season, when flu vaccines "prevented about 700,000 influenza cases and 65,000 hospitalizations" in adults 65 and older.

When to get vaccinated

Dr. Kernisan shares the CDC's guidance to "get vaccinated against influenza early in the fall (before the end of October 2026)." That means right now is a great time to make the appointment.

Quick answers

Is the flu dangerous for older adults? Yes. Aging immune systems respond less strongly, and older adults are at higher risk of hospitalization from the flu.

When should seniors get a flu shot in 2026? Early fall, before the end of October 2026, per CDC guidance cited by Dr. Kernisan.

Does the flu vaccine work for people over 65? Yes. Protection is lower than in younger adults, but it still prevents many cases and hospitalizations.

From the Indigo team

This is something we talk about with our clients' families every fall: flu shots aren't just for the person we care for, but for everyone who visits them too. If your loved one has an upcoming doctor's appointment, it's a good time to ask about their flu shot.

Coming up in Part 2 of 5: The four flu vaccines Dr. Kernisan recommends specifically for older adults, including a brand-new mRNA option approved in August 2026.

Source: Kernisan, Leslie, MD MPH. "Flu Shots for Older Adults: What to Know & Do for 2026." Better Health While Aging, September 18, 2026. https://betterhealthwhileaging.net/flu-shots-in-aging-what-to-know/

This post summarizes an article by Leslie Kernisan, MD MPH, for general education. It isn't medical advice. Talk with your or your loved one's doctor about which vaccine is right for you.