To Örebro University

Background: Observational and small randomized studies suggest that influenza vaccine may reduce future cardiovascular events in patients with cardiovascular disease.

Methods: We conducted an investigator-initiated, randomized, double-blind trial to compare inactivated influenza vaccine with saline placebo administered shortly after myocardial infarction (MI) (99.7% of patients) or high-risk stable coronary heart disease (0.3%). The primary endpoint was the composite of all-cause death, MI, or stent thrombosis at 12 months. A hierarchical testing strategy was used for the key secondary endpoints: all-cause death, cardiovascular death, MI, and stent thrombosis.

Results: Due to the Covid-19 pandemic, the data safety and monitoring board decided to halt the trial before attaining the prespecified sample size. Between October 1, 2016, and March 1, 2020, 2571 participants were randomized at 30 centers across eight countries; 1290 assigned to influenza vaccine and 1281 to placebo. Over the 12-month follow-up, the primary outcome occurred in 67 participants (5.3%) assigned influenza vaccine and 91 participants (7.2%) assigned placebo (hazard ratio, 0.72; 95% confidence interval, 0.52 to 0.99; P=0.040). Rates of all-cause death were 2.9% and 4.9% (hazard ratio, 0.59; 0.39 to 0.89; P=0.010), of cardiovascular death 2.7% and 4.5%, (hazard ratio, 0.59; 0.39 to 0.90; P=0.014), and of MI 2.0% and 2.4% (hazard ratio, 0.86; 0.50 to 1.46, P=0.57) in the influenza vaccine and placebo groups, respectively.

Conclusions: Influenza vaccination early after an MI or in high-risk coronary heart disease resulted in a lower risk of a composite of all-cause death, MI, or stent thrombosis, as well as a lower risk of all-cause death and cardiovascular death at 12 months compared with placebo.

Clinical Trial Registration: URL: http://www.clinicaltrials.gov Unique identifier: NCT02831608.