Cardioprotective effects of influenza vaccination among patients with established cardiovascular disease or at high cardiovascular risk: a systematic review and meta-analysis

Background The clinical impact of the influenza vaccination on cardiovascular outcomes in people with established cardiovascular disease (CVD) is still debated. Aim The aim of this meta-analysis was to estimate the effect of influenza vaccination on cardiovascular and cerebrovascular outcomes among patients with established CVD. Methods We systematically searched all electronic databases from inception until 15 April 2022. Primary clinical outcomes were all-cause mortality, and major adverse clinical events (MACEs). Secondary endpoints were heart failure, myocardial infarction, cardiovascular mortality, and stroke. Results Eighteen articles (five randomized trials and thirteen observational studies), with a total of 22 532 165 patients were included in the analysis. There were 217 072 participants included in the high cardiovascular risk or established CVD population (vaccinated n = 111 073 and unvaccinated n = 105 999). The mean age of the patients was 68 years old, without any difference between groups (69 vs. 71) years. At a mean follow-up of 1.5 years, the vaccinated group was associated with a lower risk of all-cause mortality [hazard ratio (HR), 0.71(95% CI, 0.63–0.80), P < 0.001], MACE [HR, 0.83(95% CI:0.72–0.96), P = 0.01], CV mortality [HR, 0.78(95% CI:0.68–0.90), P < 0.001], and MI [HR, 0.82 (95% CI:0.74–0.92), P < 0.001] compared to the unvaccinated group. While the incidence of stroke [HR, 1.03 (95% CI, 0.92–1.06), P = 0.61] and heart failure [HR, 0.74 (95% CI, 0.51–1.08), P = 0.12] did not differ between the two groups. Conclusion Influenza vaccination reduced MACEs, all-cause mortality, CV mortality, and MI. These highlighted the importance of influenza vaccination in established CVD or high cardiovascular risk.