The surprising perks and hidden benefits of getting a flu shot

Andrea Graves

New Zealand Listener·

23 Jun, 2026 06:04 PM4 mins to read

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You’re getting vaccinated against the disease on the label, but you’re also taking your immune system for a run. It’s like keeping fit. Photo / Getty Images

Last spring I got flu. Not just a nasty cold but the can’t-walk-to-the-letterbox type, influenza A. When the fevers and lacerating cough eased, my body was the remnants of a battlefield. I swore I’d start getting an annual flu vaccination.

In a happy twist, research shows my jab has
not only protected me from a repeat of the sickness but also reduced my heart attack and stroke risk. I like that so much that I had the shingles vaccine as well. It, too, has surprising perks, including dementia prevention and possibly a slower rate of ageing.

Philip Shirley, a GP and public health registrar at the University of Auckland’s Immunisation Advisory Centre, is scrutinising the evidence on this. With a flu vaccine, he says, “You’re not just stopping people from catching the flu, you’re preventing the downstream effects of having a major adverse inflammatory event.”

Heart attack and stroke can be two of those events. Spikes of both in bad flu seasons have been recognised for the past century, and a Canadian study showed people with a confirmed flu infection have 6-7 times the risk of having a heart attack in the following week, says Shirley. “We know the flu virus literally goes inside your blood vessels and can destabilise plaques. If it’s in the heart, it can cause a heart attack. In the brain, that can cause a stroke.”

Plaque is gunk that sits quietly for years inside blood vessels, and if it ruptures, the vessel can become clogged, damaging the surrounding tissue by starving it of oxygen. Heart muscle damage resulting from clogged arteries is the leading cause of death in New Zealand.

“The strongest evidence we have for the flu vaccine preventing heart attacks is giving it to people within three days of their first heart attack: if you monitor those folk for a year, they have 30% fewer repeat events.” That study ruled out what Shirley calls “the healthy vaccinee effect” that can make outcomes seem better because people who get regular vaccinations tend to be wealthier, have more formal education, not smoke, etc.

Philip Shirley: Vaccination can refresh the immune system. Photo / Supplied

The benefits extend beyond not getting flu. Research is increasingly showing that vaccination rejuvenates an ageing immune system. “The immune system is ageing along with the body, and it’s getting a little bit forgetful about some of the bugs it’s seen in the past; it’s getting a bit more sluggish,” says Shirley. “You get trained immunity from vaccines. You’re getting vaccinated against the disease on the label, but you’re also taking your immune system for a run. It’s like keeping fit. So when you encounter just a run-of-the-mill cold virus, you’re not vaccinated against it but your ability to recognise it and mount a response to it is much quicker.”

There’s less powerful evidence for trained immunity than for direct protection against the target disease. “We’re not sure how big this effect is but we think it’s real, and people are investigating this actively.”

Scientists are also exploring vaccines for broader anti-ageing effects. A recent University of Southern California study showed the shingles vaccine – for which there’s also compelling evidence of less dementia, heart disease and stroke – was linked to slower biological ageing. That showed up in lower inflammatory markers and several other molecular ageing hallmarks.

Shirley says there are early signals that certain vaccines may lessen “inflammaging”, which is persistent, low-grade inflammation related to an ageing immune system.

Whether for personal health or keeping hospital beds available, these added benefits mean vaccination makes even more sense, he says. “People who are at high risk of heart attacks would be close to the top of my list if we were expanding access to funded vaccines.” He notes Māori and Pacific people tend to have heart attacks earlier but no longer get free flu vaccines until they’re 65, unless they meet other criteria.

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