Influenza vaccination shortly after a myocardial infarction (MI) or in high-risk coronary heart disease reduces the risk of future cardiovascular events, according to findings from the IAMI trial presented at the ESC Congress 2021.
Influenza infection is known to be associated with an increased risk of cardiovascular events, and small, randomized trials and observational studies have suggested that the influenza vaccine might reduce the risk of cardiovascular events in patients with cardiovascular disease. “We have, for the first time, confirmed this in a well-powered trial, showing that the influenza vaccine works and saves lives after MI,” comments Ole Fröbert, lead author of the IAMI study.
IAMI was an investigator-initiated, double-blind, randomized, controlled trial conducted in eight countries. The 2,571 trial participants were assigned to receive either inactivated influenza vaccine or saline placebo, administered shortly after hospital admission for MI (99.7% of patients) or high-risk stable coronary heart disease (0.3%). Of note, the trial was halted before reaching the prespecified sample size owing to the COVID-19 pandemic.
At 12 months, influenza vaccination was associated with a 28% reduction in the risk of a composite of all-cause death, MI or stent thrombosis (the primary outcome) compared with placebo (5.3% versus 7.2%; HR 0.72, 95% CI 0.52–0.99, P = 0.040). Influenza vaccination also reduced by 41% both all-cause mortality (2.9% versus 4.9%; HR 0.59, 95% CI 0.39–0.89, P = 0.010) and cardiovascular mortality (2.7% versus 4.5%; HR 0.59, 95% CI 0.39–0.90, P = 0.014). Finally, an exploratory meta-analysis including data from this trial and from three previous smaller randomized trials showed a 50% reduction in the risk of cardiovascular death at 1 year in patients receiving influenza vaccination.
“We have, for the first time, confirmed … in a well-powered trial … that the influenza vaccine works and saves lives after MI”
“These findings suggest that a flu shot in hospital to patients treated for MI should be implemented,” says Fröbert. Looking to the future, Fröbert highlights the need for a better understanding of the potential mechanisms. “The influenza vaccine seems to do more than protect against influenza,” he explains, “and many indications from animal and some human studies suggest that the vaccine modulates inflammation (important in MI) and prevents (indirectly) thrombosis”.
Fröbert, O. et al. Influenza vaccination after myocardial infarction: a randomized, double-blind, placebo-controlled, multicenter trial. Circulation https://doi.org/10.1161/CIRCULATIONAHA.121.057042 (2021)
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Fernández-Ruiz, I. Flu vaccination shortly after MI reduces the risk of complications. Nat Rev Cardiol (2021). https://doi.org/10.1038/s41569-021-00620-6