WASHINGTON – Patients with heart failure who received an annual influenza vaccine for 3 years running had significantly fewer all-cause hospitalizations and significantly fewer cases of pneumonia during that time, compared with placebo-treated patients with heart failure, in a prospective, randomized, global trial with 5,129 participants.
Although the results failed to show a significant reduction in all-cause deaths linked to influenza vaccination, compared with controls during the entire 3 years of the study, the results did show a significant 21% relative mortality-risk reduction by vaccination during periods of peak influenza circulation, and a significant 23% reduction in cardiovascular deaths, compared with controls during peak seasons.
“This is the first randomized, controlled trial of influenza vaccine in patients with heart failure, and we showed that vaccination reduces deaths” during peak influenza seasons,, said during a press briefing at the annual scientific sessions of the American College of Cardiology. The results send “an important global message that patients with heart failure should receive the influenza vaccine,” said Dr. Loeb, a professor at McMaster University, Hamilton, Ont., who specializes in clinical epidemiology and infectious diseases.
Dr. Loeb admitted that he and his associates erred when they picked the time window to assess the two primary endpoints for the trial: the combined rate of cardiovascular death, nonfatal MI, and nonfatal stroke, and this combined endpoint plus hospitalizations for heart failure.
The time window they selected was the entirety of all 3 years following three annual immunizations. That was a mistake.
No flu vaccine benefit outside flu season
“We know that the influenza vaccine will not have any effect outside of when influenza is circulating. In retrospect, we should have done that,” Dr. Loeb bemoaned during his talk. He chalked up the bad choice to concern over collecting enough endpoints to see a significant between-group difference when the researchers designed the study.
For the entire 3 years of follow-up, influenza vaccination was tied to a nonsignificant 7% relative risk reduction for the first primary endpoint, and a nonsignificant 9% relative risk reduction for the second primary endpoint, he reported.
But Dr. Loeb lobbied for the relevance of several significant secondary endpoints that collectively showed a compelling pattern of benefit during his talk. These included, for the full 3-years of follow-up, important, significant reductions relative to placebo of 16% for first all-cause hospitalizations (P = .01), and a 42% relative risk reduction in first cases of pneumonia (P = .0006).
Then there were the benefits that appeared during influenza season. In that analysis, first events for the first primary endpoint fell after vaccination by a significant 18% relative to placebo. The in-season analysis also showed the significant cuts in both all-cause and cardiovascular deaths.
Despite the neutral primary endpoints, “if you look at these data as a whole I think they speak to the importance of vaccinating patients with heart failure against influenza,” Dr. Loeb maintained.
‘Totality of evidence supports vaccination’
“I agree that the totality of evidence supports influenza vaccination,” commented, professor and clinical chief of cardiology at the University of Texas Southwestern Medical Center, Dallas, who was designated discussant for the report.
“The message should be to offer influenza vaccine to patients with heart failure,” Dr. Drazner said in an interview. “Previous data on influenza vaccine in patients with heart failure were largely observational. This was a randomized, prospective, placebo-controlled trial. That’s a step forward. Proving efficacy in a randomized trial is important.”
Dr Drazner added that his institution already promotes a “strong mandate” to vaccinate patients with heart failure against influenza.
“The influenza vaccine is a very effective and cost-efficient public health measure. Preventing hospitalizations of patients with heart failure has so many benefits,” commented, vice president of professional services at Baptist Health in Paducah, Ky., and a discussant during the press briefing.
The Influenza Vaccine To Prevent Adverse Vascular Events () trial enrolled people with heart failure in New York Heart Association functional class II, III, or IV from any of 10 low- and middle-income countries including China, India, the Philippines, and multiple countries from Africa and the Middle East. They averaged 57 years of age, and slightly more than half were women.
IVVE was sponsored by McMaster University; the only commercial support that IVVE received was a free supply of influenza vaccine from Sanofi Pasteur. Dr. Loeb, Dr. Drazner, and Dr. Beavers had no disclosures.