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.