The Bonus: What Else Vaccines Protect You From

Vaccines are tested against the disease they target. But some turn out to do more: a shingles shot that may lower the risk of dementia, a flu shot that cuts deaths after a heart attack, a measles vaccine that protects children from every other infection, and two vaccines that prevent cancer.

1. Shingles vaccine and dementia

When Wales began offering a shingles vaccine on 1 September 2013, only people aged 79 on that date were eligible; people who had just turned 80 were not. That accident of timing created a near-perfect experiment: two groups of older adults almost identical except for whether they could get the vaccine.

Stanford researchers led by Pascal Geldsetzer compared more than 280,000 of them and reported in Nature on 2 April 2025 that those vaccinated were 20% less likely to be diagnosed with dementia over the next seven years. The effect was much stronger in women. A follow-up in Cell in December 2025 suggested the vaccine may also help people who already have dementia: about 30% of vaccinated patients died of it, against nearly half of the unvaccinated. “This huge protective signal was there, any which way you looked at the data,” Geldsetzer said (Stanford Medicine).

The Wales study used the older live vaccine, Zostavax. Canada now uses Shingrix, a different and more effective vaccine. Whether it has the same effect on dementia is still being studied.

2. Flu vaccine and the heart

Influenza strains the heart, and heart attacks rise during flu season. In the IAMI trial, 2,532 patients in eight countries who had just had a heart attack or a procedure to open a blocked artery were randomly given a flu shot or a placebo within 72 hours. Over the following year (American College of Cardiology summary; Frøbert et al., Circulation, 2021):

• deaths from any cause: 2.9% with the flu shot, against 4.9% with placebo;
• deaths from heart disease: 2.7% against 4.5%;
• the combined risk of death, heart attack or stent clot fell by 28%.

For anyone with heart disease, the flu shot is heart medicine.

3. Measles vaccine and every other infection

When measles vaccination began in the 1960s, childhood deaths from all infections fell, not just deaths from measles. In some poorer countries, child mortality dropped by as much as 80%. In 2015 Michael Mina and colleagues showed in Science, using data from the United States, Denmark, England and Wales back to the 1940s, that measles leaves children more vulnerable to other infections for two to three years (NPR). “The immune system kind of comes back,” Mina said. “The only problem is that it has forgotten what it once knew.”

In 2019 the same group showed how: measles wipes out 11 to 73% of a child’s existing antibodies, a process called “immune amnesia.” Preventing measles protects a child from far more than measles. See What These Diseases Do.

4. Two vaccines that prevent cancer

• HPV vaccine: in Scotland, not one case of invasive cervical cancer among women vaccinated at 12 or 13; in Sweden, 88% fewer cancers in women vaccinated before 17. See The HPV Vaccine.
• Hepatitis B vaccine: about 90% of babies infected at birth become lifelong carriers at risk of liver cancer. After Taiwan began vaccinating every newborn in 1984, liver cancer in children roughly halved. See Before the Vaccines.

5. How sure are we?

These findings are not all equally strong, and it is worth saying so plainly, because anti-vaccine writers are quick to overstate a single study when it suits them.

• Cancer prevention by HPV and hepatitis B vaccines: established, with years of population data.
• Measles and other infections: strong, from decades of data in several countries and a clear biological mechanism.
• Flu shot after a heart attack: a randomized trial, the best kind of evidence, but it was stopped early by the COVID-19 pandemic at about 60% of its planned size.
• Shingles and dementia: a very strong natural experiment, supported by other studies, but not yet a randomized trial, and based on an older vaccine.

None of these is the reason to get the vaccine. They are a bonus on top of protection from the disease itself.

6. What to do

• 65 to 70 in Ontario? The two-dose Shingrix vaccine is free from your family doctor or nurse practitioner. Outside that age range, ask your doctor or pharmacist; it is recommended for adults 50 and over.
• Heart disease? Get a flu shot every fall. Ask for it if you are in hospital with a heart attack during flu season.
• Children: two doses of measles vaccine, and HPV in Grade 7.