A JAMA Internal Medicine analysis of more than one million U.S. veterans found the protective effect extended beyond documented infections, with the largest gains in adults 75 and older.
When Ziyad Al-Aly talks to patients who arrive at his clinic with a heart attack or stroke and no obvious explanation, the story often starts the same way. "They felt under the weather for a few days, didn't test for Covid, and a few weeks later showed up in the ER with a major cardiovascular event," the Washington University in St. Louis clinician-researcher said. He thinks those events are downstream of an unrecognized SARS-CoV-2 infection. A study published Monday in JAMA Internal Medicine, based on more than one million U.S. veterans, gives that hypothesis a large-scale statistical anchor.
Among veterans who got a flu shot at a VA facility in 2024, those who also received a Covid vaccine had about a 38% lower risk of major cardiovascular events tied to a documented Covid infection over the following eight months. The more surprising number was the secondary result: roughly a 24% lower risk of major cardiac events across the board, including among people whose records contained no positive Covid test. STAT News reported the study findings.
The all-cause finding is what makes the study, published in JAMA Internal Medicine, more than another effectiveness analysis. If vaccination were only blocking severe acute illness, researchers would expect the benefit to vanish in the much larger pool of people with no recorded infection. It did not. The authors estimate the effect could translate to roughly 3,500 major cardiac events and 2,400 deaths prevented per million people each year, though the design is observational and the calculation is extrapolation, not measurement.
The protection was not distributed evenly. The largest reductions appeared in adults 75 and older and in people with chronic conditions such as kidney and lung disease, groups already known to carry the heaviest cardiovascular burden. The pattern matters because those are also the populations most likely to have atypical or asymptomatic infections, and the ones most likely to present weeks later with cardiac complications that get attributed to age or comorbidity rather than a virus.
Robert Califf, a cardiologist and former FDA commissioner, wrote an accompanying commentary in JAMA Internal Medicine and endorsed the broader direction. He noted that other non-Covid vaccines, including influenza shots, have also shown cardiovascular benefit in prior studies, which fits a model in which vaccination reduces the inflammatory insults that drive cardiac events. He flagged the weakest link: ascertainment of Covid infection. With at-home testing largely gone from clinical records, the study can only count infections that were tested and logged, and the real number of unrecognized infections is almost certainly higher. His commentary does not dismiss the result; it qualifies it.
The study has other limits worth naming. The cohort is VA flu-vaccine recipients, overwhelmingly older men with high rates of chronic disease, so the findings do not translate cleanly to younger adults, women, or healthier populations. The design is observational, and although the researchers adjusted for a long list of confounders, healthy-vaccinee bias and unmeasured differences between vaccinated and unvaccinated groups can never be fully ruled out. The 38% and 24% figures are relative reductions, and the absolute number of events prevented depends on a person's underlying risk. None of that erases the signal, but it is the difference between a hypothesis and a guideline.
The result also reframes an old safety debate. Earlier concerns focused on mRNA-vaccine-associated myocarditis, mostly in young men, and they were real. A separate body of work, including studies in the American Heart Association's Circulation journal, has shown that myocarditis following Covid infection tends to be more severe than myocarditis following vaccination, and that the cardiac risk-benefit balance is highly age-dependent. Al-Aly's finding sits on the other side of that ledger: in the older, sicker populations who actually account for the bulk of cardiovascular mortality, the dominant effect of vaccination now appears to be protective, not risky.
What to watch next is whether the all-cause reduction holds up in cohorts that look more like the general population, and whether the effect persists as SARS-CoV-2 continues to evolve. The veterans in the 2024 cohort were exposed to the variants circulating then, and the virus is not standing still. For now, the practical implication is narrower than the headline number and more personal than the population estimate. For people in the high-benefit groups, especially those 75 and older and those living with chronic kidney or lung disease, a Covid shot appears to do more than guard against a bad case of the virus. It may also be quietly lowering the chance that the next chest pain lands them in the emergency room.