News · Heart & Metabolic
COVID vaccine tied to fewer heart events in over-75s
A JAMA Internal Medicine study of 1,039,659 US veterans found the 2024-2025 COVID vaccine tracked with fewer heart attacks, strokes and cardiovascular deaths, with the benefit concentrated in the oldest.
Based on a peer-reviewed cohort study in JAMA Internal Medicine
- Researchers used US Department of Veterans Affairs records covering 1,039,659 people who got a flu shot between September and December 2024, publishing in JAMA Internal Medicine.
- The comparison was people who took the COVID vaccine alongside the flu shot against people who took the flu shot alone, so both groups had already chosen to be vaccinated for something.
- Vaccine effectiveness against COVID-associated heart attack, stroke, heart failure hospitalization or cardiovascular death was 37.7% at eight months (95% CI, 18.2%-54.9%).
- The benefit was statistically significant only in people older than 75, where effectiveness reached 50.7% and the absolute gain was largest at 5.5 fewer events per 10,000.
- No significant effect was seen in people under 65, or in the 65-to-75 group.
- Absolute numbers are small: 2.0 fewer COVID-associated events per 10,000 people overall.
- All-cause heart events fell much more than COVID-specific ones, at 23.7 fewer per 10,000, which the authors read as undetected infection doing hidden damage.
- This is a target trial emulation using medical records, not a randomized trial, and the population is 91.8% men with a mean age of 70.
A vaccine is judged on whether it stops the infection. This one was judged on something further downstream: whether the people who took it had fewer heart attacks and strokes afterwards. A study in JAMA Internal Medicine, published by the American Medical Association, followed more than a million veterans to find out.
Among 1,039,659 participants who received influenza vaccine, the COVID-19 vaccine was associated with lower risk of COVID-19-associated major adverse cardiovascular events.
Why heart events are the outcome to watch
The link runs through infection. COVID raises the short-term risk of heart attack, stroke and heart failure, so anything that prevents or blunts infection should show up later as fewer of those events.
COVID-19 vaccines were previously shown to reduce risk of major adverse cardiovascular events. The open question is whether that still holds: whether the 2024-2025 COVID-19 vaccine continues to reduce COVID-19-associated cardiovascular events in the context of evolving variants and widespread population immunity is unknown.
That framing matters. Most of the population now has immunity from infection, vaccination or both, and each new variant is further from the original. A benefit measured in 2021 does not automatically survive to 2026.
The comparison that makes it credible
The hardest problem in vaccine research is that people who get vaccinated are different from people who do not, in ways that also predict heart attacks.
This study sidestepped much of that. It was a target-trial emulation using Department of Veterans Affairs electronic health records, comparing same-day coadministration of the 2024-2025 COVID-19 and influenza vaccines against influenza vaccine alone.
Everyone in the study turned up for a flu shot. The only difference is what else they took while they were there. That does not eliminate the problem, but it removes its largest component.
What the numbers came to
At eight months, the COVID-19 vaccine was associated with lower risk of COVID-19-associated cardiovascular events, with vaccine effectiveness of 37.7%.
The age pattern is the finding that deserves attention. The benefit held up only in individuals older than 75 years, at 50.7%, a group that also experienced the largest absolute risk reduction. No vaccine effectiveness was observed among those younger than 65 years or aged 65 to 75 years.
That is most likely arithmetic rather than biology. Younger people have very few such events to prevent, so a real effect can hide in the noise.
The number that is larger than expected
The COVID-specific benefit is modest in absolute terms: a risk difference per 10 000 persons, 2.0. Two events avoided in every ten thousand people.
The all-cause figures are not modest. Looking at all-cause heart events suggested substantially larger absolute risk reductions, at 23.7 per ten thousand.
The authors’ reading is that the vaccine’s protective association extends to the hidden burden of undetected SARS-CoV-2 and its sequelae: infections nobody tested for, and so nobody coded as COVID-related, still doing damage. It is a plausible account of a real gap. It is not something a cohort study can demonstrate.
What this cohort cannot show
Nobody was randomized. Matching and weighting balance what the records captured; they cannot balance the reasons one veteran accepted a second injection and another declined.
The population is also specific: US veterans, 91.8% men, mean age 70. Whether the same pattern holds in younger women is not a question this data can answer.
Eight months is the whole window. The authors keep their claim inside it, concluding that receipt of the vaccine was associated with reduced risk, with reductions most prominent in those 75 years or older and those with comorbidities.
For a reader over 75, that is the sentence that matters. For a reader of 40, this particular study found nothing either way.
People also ask
Does this show the vaccine protects the heart directly?
Not directly. The mechanism the authors describe is indirect: COVID infection raises the risk of heart attack, stroke and heart failure, so preventing or blunting infection prevents those downstream events. The study measured COVID-associated cardiovascular events, meaning events occurring around a documented infection. Nothing here suggests the vaccine acts on the heart itself.
Why compare against people who got a flu shot rather than nobody?
Because it removes the largest confounder in vaccine research. People who seek out vaccination differ from people who avoid it in health literacy, medical contact and general caution, and those differences also predict heart attacks. Comparing flu-shot-plus-COVID against flu-shot-alone means both groups already showed up for a vaccine. It is the closest an observational design gets to a fair comparison.
Why did it only work in the over-75s?
The most likely explanation is arithmetic rather than biology. Younger people have very few COVID-associated cardiovascular events to prevent, so even a real effect produces too few cases to detect. Older adults have far more events, so the same protection shows up clearly and translates into a bigger absolute gain. The study cannot rule out a genuine difference in how well the vaccine works by age.
How big is the benefit in practical terms?
Modest for COVID-specific events: about 2 fewer per 10,000 people over eight months overall, rising to 5.5 per 10,000 in the over-75s. The all-cause figure is much larger at 23.7 per 10,000. The authors interpret the gap as infections that were never tested for and so never recorded as COVID-associated, though a cohort study cannot prove that.
What are the main limitations?
It is observational, so residual differences between the groups may remain despite adjustment. The population is US veterans, 91.8% men, with a mean age of 70, which is not the general population. And an eight-month window cannot say anything about longer-term outcomes.