Heart failure (HF) patients who received an annual flu shot had lower rates of pneumonia and hospitalization on a year-round basis and a reduction in major cardiovascular events during peak flu season, based on results from the IVVE trial presented April 3 at ACC.22. However, no significant reductions in rates of major cardiovascular events were observed on a year-round basis, researchers said.

A total of 5,129 patients with HF were enrolled in the study, which was conducted in 10 countries across Asia, Africa and the Middle East where getting a flu shot is not routine for most people. None of the participants had received a flu shot more than once in the three years prior to the trial. Researchers randomized participants to receive a flu shot or placebo annually for up to three years. The trial's primary endpoint was a composite of death from cardiovascular causes, nonfatal heart attack or nonfatal stroke. Its co-primary endpoint included a composite of any of these events plus hospitalization for HF.

Overall, the composite primary endpoint occurred in 691 participants and 1,470 experienced the composite co-primary endpoint. When analyzed on a year-round basis there was no significant difference in the rates of these events between those who had received a flu vaccine and those who received the placebo. However, separate analyses of hospitalization, pneumonia and other respiratory outcomes found that rates of pneumonia were 42% lower and hospitalizations were 15% lower in the flu shot group. Researchers also found a significant reduction in the first primary endpoint – as well as reductions in all-cause death and cardiovascular death – in favor of the flu vaccine during months of the year when infection with influenza virus was common.

In contrast, there was no significant difference in these endpoints between groups during periods of the year when influenza circulation was low. Based on these results, researchers said the flu vaccine did help to protect patients from influenza complications, including cardiovascular events.

"Although our prespecified endpoints were not significant, our data suggest that there's a clinical benefit [to getting a flu shot] given the clear reduction in pneumonia, moderate reduction in hospitalization and reduction in vascular events and deaths during periods of peak influenza," said Mark Loeb, MD, the study's lead author. "When taken together with previous trials and observational studies, the collective data demonstrate there is a substantial benefit to receiving a flu vaccine for people with heart failure."

While the study was conducted in countries where the flu vaccine is not widely available, Loeb said the results could likely be generalizable even in Western countries where flu vaccine uptake is higher. He also noted that the study was stopped early in four countries due to the COVID-19 pandemic and suggested that additional trials and large-scale observational studies could further clarify the health benefits of influenza vaccination in people with cardiovascular disease.

Clinical Topics: Heart Failure and Cardiomyopathies, Acute Heart Failure

Keywords: ACC Annual Scientific Session, ACC22, Influenza Vaccines, Heart Failure, Influenza, Human, Hemagglutination Inhibition Tests

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