Updated COVID-19 Vaccines Linked to Lower Cardiovascular Risk in New Study
A large-scale study of U.S. veterans reveals that updated 2024-2025 COVID-19 vaccines do not increase cardiovascular risks, instead showing a 37.7% relative drop in severe heart events among vaccinated older adults.
COVID-19 affects far more than just the respiratory system, a fact known since 2020. Research has established a clear link between COVID-19 infection and an elevated risk of severe cardiovascular events, including heart attacks, ischemic strokes, heart failure, and cardiovascular mortality. This relative risk peaks notably during the first week following diagnosis and gradually declines over the subsequent months.
While COVID-19 vaccines have been associated with a slight increase in the risk of myocarditis (heart muscle inflammation), this phenomenon remains rare and generally milder than myocarditis caused by the virus itself. The risk of vaccine-related myocarditis is highest among young males shortly after vaccination. However, previous studies have not supported claims of an overall cardiovascular risk increase following vaccination. On the contrary, a massive study conducted in England revealed that among vaccinated individuals, the incidence of vascular-damaging events post-vaccination was generally comparable to or lower than pre-vaccination levels. An analysis of British health service data indicated that prior vaccination was linked to a degree of protection against life-threatening blood clots following COVID-19 diagnosis. A plausible explanation is that vaccination mitigates infection severity, thereby reducing inflammation, vascular damage, and pro-clotting mechanisms.
Assessing the 2024-2025 Vaccine Efficacy
Because the coronavirus has continually mutated and current variants typically cause milder illness compared to earlier strains—coupled with widespread population immunity from prior infections, vaccinations, or both—it remained unclear whether the cardiovascular benefits observed during the initial pandemic years persisted for the 2024-2025 season. A large-scale new study was designed specifically to answer this question.
To overcome potential observational biases, researchers utilized health data from U.S. military veterans and simulated a randomized trial structure using target trial emulation. They defined an ideal trial framework and structured observational data analysis to mimic it as closely as possible. The study compared older adults who received both a flu shot and an updated 2024-2025 COVID-19 vaccine on the same day against peers who received only the influenza vaccine. Comparing two vaccinated cohorts was designed to minimize "healthy vaccinee bias"—the confounding scenario where individuals who choose to vaccinate inherently differ from those who do not, such as having healthier lifestyles or differing healthcare-seeking behaviors. Conversely, it also accounts for the opposite bias where individuals in poorer health might seek out more vaccinations.
A total of approximately 1.04 million participants were included in the analysis: roughly 349,000 received both COVID-19 and flu vaccines, while approximately 691,000 received only the flu shot. Individuals who had been vaccinated against or infected with COVID-19 within the 90 days preceding the study were excluded to minimize the residual impact of prior immunizations or recent infections. The follow-up period spanned eight months.
Statistical Adjustments and Findings
Researchers implemented rigorous statistical adjustments to account for known baseline differences between groups, including age, underlying medical conditions, prior screenings, and healthcare utilization habits. They also accounted for crossover cases, where individuals initially receiving only the flu shot subsequently received a COVID-19 vaccine during follow-up. Sensitivity analyses, such as excluding the first two weeks post-vaccination when full immunity has not yet developed, yielded consistent results, reinforcing confidence in the findings while acknowledging potential unmeasured confounders.
The results demonstrated a clear reduction in severe cardiovascular events among vaccinated individuals. A relative decrease of 37.7 percent was observed in cardiovascular events occurring in close temporal proximity to a COVID-19 diagnosis. In absolute terms, this translates to roughly one fewer event per approximately 5,000 vaccinated individuals. This reduction was primarily driven by lower cardiovascular mortality, fewer heart attacks, and reduced hospitalizations for heart failure. A decrease in stroke cases was also noted, though it did not reach statistical significance.
Subgroup analyses indicated that the benefits were most pronounced among high-risk individuals and those with underlying health conditions. The decrease in severe cardiovascular events surrounding a COVID-19 diagnosis was statistically significant only among adults aged 75 and older. The researchers clarified that they did not attribute the cardiovascular events directly to the vaccines, but rather tracked events like heart attacks, strokes, cardiovascular deaths, or heart failure hospitalizations occurring shortly after confirmed COVID-19 diagnoses. This distinction means that while relative risk reductions are comparable across groups, the absolute number of averted events is significantly higher for populations facing elevated baseline risks.
Broad Health Outcomes and Overall Risk Balance
In addition to the primary analysis focusing on acute cardiovascular events near confirmed COVID-19 diagnoses, researchers conducted a broader secondary analysis examining all-cause severe cardiovascular events, all-cause hospitalizations, and all-cause mortality. This approach aimed to capture potential harms from undiagnosed or undocumented COVID-19 infections. Even under this broader analysis, vaccinated individuals exhibited lower risks: approximately one fewer severe event per 400 to 450 vaccine recipients, one fewer hospitalization per approximately 330 recipients, and one fewer death per 600 to 650 recipients.
However, the authors emphasize that these estimates stem from observational research and do not constitute direct proof that every single event was prevented solely by the vaccine. Consequently, they serve as an indicator of a lower overall risk profile rather than a direct measurement of hidden COVID-19 harms.
«The significance of this study lies in shifting the contemporary discourse regarding COVID-19 vaccines. Instead of asking solely whether they might pose cardiac risks, it is more accurate to examine the overall risk balance following receipt of updated vaccines. This study found no increase in severe cardiovascular events following the new vaccine. On the contrary, the findings point toward risk reduction for such events, particularly among older adults and individuals with high baseline risk.»
The study's findings indicate that vaccination does not introduce cumulative risk, but rather serves as a valuable tool to mitigate some of the severe consequences of COVID-19 among vulnerable populations.
