Influenza Vaccination After Myocardial Infarction Lowers Risk of Future CV Events

Ole Fröbert, MD, PhD

Previous research on influenza epidemics from 1915 - 1929 found a positive association between influenza with the risk of cardiovascular events.

However, although there is a known temporal association, there remains a need for large clinical trial evidence to determine if influenza vaccination is effective in prevention of future CV events in patients with cardiovascular disease (CVD).

As a result, investigators in the Influenza vaccination After Myocardial Infarction (IAMI) trial hypothesized that influenza vaccination may result in reduction of incidence of death, myocardial infarction (MI), and stent thrombosis in patients with recent MI or high-risk coronary disease.

The team, led by Ole Fröbert, MD, PhD, Örebro University, Faculty of Health Department of Cardiology, found early influenza vaccination after MI showed lower risk of a composite of all-cause death, MI, or stent thrombosis, with a lower risk of all-cause and CV death at 12 months, in comparison to placebo.

Methods

IAMI was a randomized, double-blind, investigator-initiated trial, designed for evaluation of the efficacy of the influenza vaccine following MI or percutaneous coronary intervention (PCI) in high-risk patients with coronary artery disease.

It was conducted at 30 centers in 8 countries, including Sweden, Denmark, Norway, Latvia, the UK, Czech Republic, Bangladesh and Australia from October 2020.

Eligible participants had ST-elevation myocardial infarction (STEMI) or non-STEMI and completed coronary angiography or PCI and were ≥18 years of age. Exclusions occurred if patients had received an influenza vaccination within the past 12 months, intended to be vaccinated during influenza season, or met other exclusion criteria.

Participants were randomized 1:1 to either the influenza vaccine or placebo. Primary outcomes included composite of all-cause death, MI, or stent thrombosis at 12 months post-randomization.

In addition, a hierarchical testing strategy was used for the key secondary efficacy endpoints including all-cause death, CVD, MI, and stent thrombosis. Participants documented reactions for vaccination for 1 week, with serious adverse events recorded through the 12-month follow-up timeline.

Results

In April 2020, the data and safety monitoring board of the study halted the trial due to the COVID-19 pandemic, before the recruitment sample size was met. They noted transmission of influenza was expected to decrease and COVID-19 related deaths would most likely become common in both arms of the trial, affecting interpretation of the results.

Due to this, 6696 patients were screened from October 2016 - March 2020 and 2571 participants were randomized.Of this patient population, 1290 participants were assigned to the influenza vaccine and 1281 to the placebo group.

Patient data show a mean age of 59.9±11.2 years, with 462 (18.2%) female and 1348 (54.5%) with STEMI and 1119 (45.2%) with non-STEMI. Further, 1868 (74.3%) were treated with PCI.

Investigators found the primary endpoint transpired in 67 participants (5.3%) assigned to the influenza vaccine and 91 participants (7.2%) assigned to the placebo group (hazard ratio, 0.72; 95% CI, 0.52 - 0.99, P = .040).

As the secondary endpoint, investigators observed rates of all-cause death were 2.9% in the influenza vaccine group and 4.9% in the placebo group (HR 0.59; 95% CI, 0.39 - 0.90, P = .014).

Further, rates of MI were 2.0% in the influenza vaccine group and 2.4% in the placebo group (HR 0.86; 95% CI, 0.50 - 1.46, P = .57).

Data show causes of death were mainly cardiovascular and none of the 8 patients in the stable coronary artery disease group experienced an event.

Conclusion

Investigators concluded the findings show influenza vaccination administered within 72 hours of hospitalization in patients with MI or high-risk coronary heart disease lowered risk at 12-months of the composite primary outcome and a lower risk of all-cause death and CVD, in comparison to placebo.

“The findings of the IAMI study indicate that in-hospital vaccination after MI during the influenza season is safe and offers protection equivalent to standard therapies like statins and angiotensin-converting enzyme inhibitors,” investigators wrote. “In-hospital influenza vaccination as routine following MI will likely also lead to higher patient treatment compliance.”

The study, “Influenza Vaccination after Myocardial Infarction: A Randomized, Double-Blind, Placebo-Controlled, Multicenter Trial,” was published online in Circulation.