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April 03, 2022
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Flu shot yields mixed findings in HF, with some seasonal CV benefit

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WASHINGTON — People with HF who received an annual influenza vaccine had a reduction in major CV events during peak influenza season and lower rates of hospitalization and pneumonia on a year-round basis, according to the IVVE study.

IVVE was a randomized controlled trial of an influenza vaccine to prevent adverse CV events in 5,000 participants with HF who received a vaccine or placebo over three influenza seasons. The global trial, which was conducted in 10 countries across Africa, Asia and the Middle East, did not meet its co-primary endpoints, which were focused on major adverse CV events on a year-round basis, but showed benefit in some secondary endpoints, including a 16% reduction in risk for all hospitalizations and 42% reduction in risk for pneumonia.

Flu vaccine
Source: Adobe Stock

However, taken together, “it speaks to the importance of vaccinating patients with HF against influenza,” Mark Loeb, MD, the Michael G. DeGroote chair in infectious diseases at McMaster University, Ontario, Canada, said during a late-breaking clinical trial presentation at the American College of Cardiology Scientific Session.

This is the first randomized controlled trial to assess the benefits of the influenza vaccine in people with HF, according to an ACC press release.

The pragmatic, double-blind, randomized trial included 5,129 adults (mean age, 57 years; 51% women) with HF in 10 countries where influenza vaccines are not common. Most participants had NYHA class II or III HF. Thirty-one percent had severe left ventricular dysfunction (LV ejection fraction 30%) and 22% had preserved EF (> 50%).

Those enrolled previously received an influenza vaccine not more than once in the previous 3 years. Participants were randomly assigned to receive an influenza vaccine (0.5 ml intramuscular dose of inactivated vaccine; Vaxigrip) or placebo (0.5 ml saline) annually for up to 3 years; they were also allowed to get the vaccine outside of the trial, but Loeb said only a fraction did. Researchers then tracked outcomes for a median of 3 years.

Outcomes at 3 years in those who received a vaccine compared with placebo were as follows:

  • First primary outcome – CV death, nonfatal MI or nonfatal stroke: 14.8% vs. 16%; HR = 0.93 (95% CI, 0.81-1.07); P = .3
  • Second primary outcome – CV death, nonfatal MI, nonfatal stroke or HF hospitalization: 20.3% vs. 22.1%; HR = 0.91 (95% CI, 0.81-1.03); P = .13
  • All-cause mortality: 16.7% vs. 18.4%; HR = 0.9 (95% CI, 0.79-1.03); P = .13
  • CV mortality: 13% vs. 14.6%; HR = 0.89 (95% CI, 0.77-1.04); P = .13
  • All hospitalizations: 15.1% vs. 17.6%; HR = 0.84 (95% CI, 0.74-0.97); P = .01
  • HF hospitalizations: 9.4% vs. 10.7%; HR = 0.88 (95% CI, 0.74-1.05); P = .15
  • Pneumonia: 2.4% vs. 4%; HR = 0.58 (95% CI, 0.42-0.8); P = .0006

“There was no significant difference in the primary outcomes between participants assigned to influenza vaccine vs. placebo. Secondary outcomes of pneumonia and hospitalization were reduced in the influenza vaccine group,” Loeb said.

When the researchers evaluated events that occurred during peak influenza season compared with non-peak periods, they found a significant reduction in the first primary outcome (7.7% vs. 9.4%; HR = 0.82; 95% CI, 0.68-0.99), all deaths (8.4% vs. 10.6%; HR = 0.79; 95% CI, 0.66-0.95), CV deaths (6.7% vs. 8.7%; HR = 0.77; 95% CI, 0.63-0.94) and pneumonia (1.1% vs. 2.1%; HR = 0.51; 95% CI, 0.32-0.81) in the influenza vaccine group compared with placebo.

Loeb said many of the effects found during peak flu circulation disappeared outside of it.