Influenza vaccination and the risk of myocardial infarction: a meta-epidemiology study

Background. The association between influenza vaccination and the risk of myocardial infarction (MI) remains incompletely characterized, particularly in real-world populations. We conducted a meta-epidemiological study to evaluate the association between influenza vaccination and incident MI using evidence from observational studies.

Methods. We systematically searched PubMed, Embase, and the Cochrane Library from inception to July 16, 2025 for cohort and case-control studies examining influenza vaccination and MI. Adjusted effect estimates were extracted and pooled as odds ratios (ORs) using random-effects models. Study quality was assessed with the Newcastle–Ottawa Scale. Subgroup analyses and meta-regression were performed to explore potential sources of heterogeneity, and publication bias was assessed using funnel plots and Egger’s test.

Results. Fifteen studies (seven cohort studies, seven case-control studies, and one self-controlled case-series) involving 23,484,167 individuals were included. Influenza vaccination was associated with lower odds of MI compared with no vaccination (OR = 0.82; 95% CI: 0.78–0.86; I² = 65.6%; P < 0.001). The direction of association was consistent across study designs, age categories, and MI history. Subgroup estimates were broadly comparable, although several analyses were based on a limited number of studies and should be interpreted with caution. Meta-regression did not identify study design, age, prior MI, or follow-up duration as significant sources of heterogeneity. No significant publication bias was detected.

Conclusions. Influenza vaccination is associated with lower odds of myocardial infarction in observational studies. While causal inference cannot be established, these findings support the potential role of influenza vaccination in cardiovascular risk prevention and highlight the need for further well-designed studies to clarify the nature and durability of this association.