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WASHINGTON -- Influenza vaccines did not appear to prevent adverse cardiovascular events in patients with heart failure in low and middle income countries, a researcher said here.

After either the influenza vaccine or placebo, there was no significant difference in the percentage of patients experiencing a composite outcome of cardiovascular death, non-fatal myocardial infarction (MI), or non-fatal stroke (14.8% vs 16%, respectively), said Mark Loeb, MD, of McMaster University in Hamilton, Ontario.

And a similar proportion of patients experienced this composite outcome or hospitalization for heart failure (20.3% vs 22.1%), Loeb said in his virtual oral presentation at the scientific session of the American College of Cardiology.

The researchers considered that because influenza is associated with an increase in the risk of cardiac and other vascular events, then vaccination against influenza might reduce these types of complications.

The (IVVE) trial took place from 2016 to 2019 in 10 countries in parts of Asia, the Middle East, and Africa, where influenza vaccination is uncommon. Researchers randomly assigned participants with to receive either an inactivated influenza vaccine (trivalent or quadrivalent if available) or placebo annually for up to 3 years.

Patients who reported having received at least two influenza vaccines in the previous 3 years were excluded; during the trial, participants were allowed to receive influenza vaccine outside of the trial protocol.

Loeb and colleagues assigned 2,560 participants to the vaccine group and 2,569 to placebo. Mean age of the participants was about 57, and 51.4% were women. Almost all (95.7%) had NYHA Class II or III heart failure, and participants were followed for a median of 2.4 years.

While there were no significant differences in the primary endpoints, Loeb noted that there was a significant between-group difference in the secondary outcomes of pneumonia and hospitalization. About 2.4% of the vaccinated cohort were diagnosed with pneumonia compared with 4% of the placebo group (P=0.0006), he reported in his presentation and at a featured press conference.

About 21.8% of the vaccinated cohort were hospitalized during the 3 years of the study compared with 26.1% of the patients in the placebo arm (P=0.001).

When examining peak influenza circulation, the influenza vaccine was associated with reduction in all deaths and in cardiovascular deaths, Loeb said. There was also a decrease in hospitalizations during the peak of the influenza season if the individual had been vaccinated.

"In those high-risk periods, we know that the flu vaccine is a very effective, cost-efficient public health measure that is broadly applicable," said Craig Beavers, PharmD, of Baptist Health System in Paducah, Kentucky, noting the reductions in deaths and hospitalizations during peak circulation.

"Any time that you can really prevent a heart failure patient from coming into the hospital has so many benefits, for a variety of reasons," added Beavers, who was designated discussant during the press conference.

He noted that patient "transitions can get messed up, guideline-directed medical therapy can go awry in those transitions," so anything that can be done to stack things in favor of the patient is beneficial. "This is a clearly easy and effective means of providing a good, solid public health measure."

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