COVID Vaccine Linked to Newly Identified Side Effect, Older Adults More Likely to Experience It

Most people think of COVID vaccines as protection against getting sick. A landmark study published June 15, 2026, in JAMA Internal Medicine found something far more significant: the vaccine dramatically reduces the risk of heart attacks, strokes, and cardiovascular deaths. The study followed more than one million U.S. veterans, and the results surprised even the researchers who ran it.

This article was created with the assistance of AI and reviewed by our editorial team for accuracy and clarity.

Researchers Tracked Over 1 Million Veterans Across Eight Months

Scientists analyzed health records from more than one million veterans who received flu shots at VA facilities between September and December 2024. About one-third of those veterans also received a COVID-19 vaccine on the same day, creating a natural comparison group. Researchers then tracked both groups for eight months, monitoring for heart attacks, strokes, heart failure hospitalizations, and cardiovascular deaths.

COVID Vaccine Reduced Cardiac Events Tied to the Virus by Nearly 38%

Veterans who received the 2024–2025 COVID vaccine had a roughly 38% lower risk of COVID-associated major cardiovascular events compared to those who skipped it, according to the STAT News report on the study. That category includes heart attacks, strokes, heart failure requiring hospitalization, and deaths directly linked to cardiovascular causes. The protection held across different vaccine types, covering both mRNA formulas and other available options.

Adults 75 and Older Saw the Strongest Heart Protection of Any Group

The cardioprotective effect was not evenly distributed. Veterans aged 75 and older showed the most significant benefit, as did those living with chronic conditions like kidney and lung disease. According to Military.com, these are the groups with the most to gain from staying current on COVID vaccination. The pattern suggests the vaccine may provide the greatest benefit precisely where cardiovascular risk is already elevated.

The Vaccine Also Cut All-Cause Cardiac Events by 24%, Even Without a COVID Diagnosis

The finding that stunned researchers most had nothing to do with documented COVID infections. Vaccinated veterans showed a 24% reduction in all-cause cardiac events, including cases with no recorded COVID diagnosis at all. Scientists had not anticipated protection that extended beyond infection-linked events. Study co-author Ziyad Al-Aly suggested that some veterans may have had undetected COVID, brushing off symptoms as feeling “under the weather” before a cardiac event, followed weeks later.

COVID Infects Blood Vessels, Not Just Lungs, Triggering Dangerous Inflammation

To understand why the vaccine protects the heart, it helps to understand what COVID does to the body. The virus does not stay confined to the respiratory system. It binds to receptors lining blood vessel walls, triggering an immune response that can spiral into dangerous inflammation. For some people, the immune system overreacts, damaging the heart’s rhythm, forming blood clots, and in severe cases triggering life-threatening heart failure. The vaccine interrupts that chain of events before it begins.

Long COVID Keeps Damaging the Body Months or Years After Infection Clears

COVID’s cardiovascular toll does not always arrive during acute illness. Long COVID, which the CDC describes as symptoms lasting months or years after infection, includes fatigue, breathing difficulties, and cognitive problems like brain fog. In some individuals, it leads to disability. A heavily mutated new variant was detected across 25 states as recently as March 2026, a reminder that the virus remains active and continues to expose millions to these downstream risks.

The Study Estimates 3,500 Prevented Heart Events Per Million People Vaccinated Annually

Researchers translated the percentage reductions into concrete numbers. For every one million people vaccinated, the vaccine is estimated to prevent roughly 3,500 major cardiac events and approximately 2,400 deaths per year, according to analysis cited by TechTimes. Those figures cover cardiovascular events across the board, not just those tied to a confirmed COVID diagnosis. The numbers frame vaccine uptake as a public health decision with measurable consequences at scale.

Myocarditis Risk From the Updated Vaccine Is Now at Background Rates

A longstanding concern about COVID vaccines has been myocarditis, an inflammation of the heart muscle reported in some younger males after earlier mRNA doses. The 2024–2025 and 2025–2026 vaccine formulations now show myocarditis rates at or below two cases per million doses, statistically indistinguishable from the general population’s baseline. Multiple large studies, including a 46-million-person analysis from England, consistently show vaccination reduces rather than increases cardiovascular risk overall.

The Study Makes the Case for Staying Current on COVID Vaccines, Especially After 75

This study does not change the basic advice around COVID vaccination. It reinforces it with the strongest cardiovascular evidence yet. For adults over 75 and those with chronic conditions, the protection is measurable, consistent across a million-person dataset, and extends well beyond respiratory illness. The researchers stated that the findings offer timely evidence for clinical and public health discussions about updated COVID vaccines in the current epidemiologic environment. The data has arrived. The decision is straightforward.