Flu shot reduces risk of cardiovascular events

Getting the seasonal influenza vaccine can reduce the risk of serious cardiovascular events like heart attacks and stroke, according to the latest research from Canada.

Researchers combined an earlier meta-analysis of randomized controlled trials for the flu shot with data from last year’s Influenza Vaccination After Myocardial Infarction (IAMI) trial and found that participants who had the flu shot had a 34% lower risk of major cardiovascular events.

The findings, published last week on the 29th of April in JAMA, by the University of Toronto, also showed that the risk was 45% lower for flu shot recipients among those deemed high risk due to an existing heart problem.

Viral respiratory infections, including those due to influenza, increase the risk for pneumonia and systemic illness that can precipitate fatal and nonfatal cardiovascular events and similarly, underlying cardiovascular disease is also a risk factor for influenza infection, downstream cardiopulmonary complications, and mortality from respiratory infections.

Lead author, Jacob Udell, said that in their preceding systematic review and meta-analysis, his team found that influenza vaccination was associated with a lower risk of fatal and nonfatal cardiovascular events within a year of getting the shot.

“Our prior meta-analysis underpinned the need for a large multicentre randomised control trial, powered for cardiovascular outcomes, to confirm our findings,” Mr Udell said.

The subsequent IAMI trial randomized 2532 patients with recent myocardial infarction to influenza vaccine or placebo and showed a lower risk of composite cardiovascular events.

“Although the study was terminated early because of the COVID pandemic, with approximately 60% of planned randomisation, IAMI prospectively confirmed our meta-analysis, while reducing the percentage of variation across the included studies because of heterogeneity to 19%,” he explained.

“With the addition of the most recent RCT data, we now also observe a significant interaction between the benefits of influenza vaccination for reducing cardiovascular mortality based on underlying cardiovascular risk.

“Specifically, among patients with a recent ACS, the risk reduction of cardiovascular death is over 50% among those who received seasonal influenza vaccine.”

The meta-analysis featured the results from six RCTs which collectively included data from 9001 adults and showed that only 3.6% of vaccinated patients developed a major adverse cardiovascular event within 12 months, compared with 5.4% of those who received placebo or control.

The researchers highlighted the importance of evaluating new influenza vaccine platforms for their potential impact on cardiovascular outcomes and were optimistic about the unlooked-for benefits of COVID inspired vaccine research.

“The potential risk reduction in major adverse cardiovascular events and cardiovascular mortality with an influenza vaccine is already sizeable… it is likely that the forthcoming improved vaccine technologies have the potential to increase this protective benefit,” Mr Udell said.

“Until then, we urge clinicians to continue counselling their high-risk patients on the cardiovascular benefits of seasonal influenza vaccination, especially given the historically low uptake of this low-cost and well-tolerated intervention.”