Annual flu jab in HF patients may lower hospitalization, pneumonia risk

An annual influenza vaccination does not lower the risk of cardiovascular (CV) outcomes in patients with heart failure (HF), though it may reduce the risk of pneumonia and hospitalization, according to results of the IVVE study presented at ACC.22.

“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 study lead author Professor Mark Loeb, Michael G. DeGroote chair in infectious diseases at McMaster University in Ontario, Canada.

This multinational*, double-blind study involved 5,129 adults (mean age 57.2 years, 51.4 percent female) with HF (New York Heart Association class II–IV; 95.7 percent had class II–III HF). They were randomized 1:1 to receive an inactivated influenza vaccine (trivalent or quadrivalent) or placebo annually for 3 years. Receipt of an influenza vaccine in 2 of the previous 3 years was criteria for exclusion. Receipt of influenza vaccination outside the trial was allowed. The participants were followed up for a median 2.4 years.

Sixty-five percent of patients had a history of hypertension, about 23 percent had diabetes, and 21 percent a prior myocardial infarction (MI). About 72 percent were on ACE** inhibitors or ARBs**, 60 percent on beta blockers, and 60 percent on aspirin or thienopyridines.  

A total of 691 participants experienced the primary outcome of a composite of CV death, non-fatal MI, or non-fatal stroke, while 1,470 participants experienced primary outcome events or hospitalization for HF (co-primary outcome). There were 605 CV deaths and 523 HF hospitalizations.

The composite of CV death, non-fatal MI, or non-fatal stroke did not significantly differ between patients who received the influenza vaccine or placebo (14.8 percent vs 16.0 percent; hazard ratio [HR], 0.93, 95 percent confidence interval [CI], 0.81–1.07; p=0.30). [ACC.21, abstract 22-LBCT-15268-ACC]

The composite of the co-primary outcome also did not significantly differ between vaccine and placebo recipients (20.3 percent vs 22.1 percent; HR, 0.91, 95 percent CI, 0.81–1.03; p=0.13).

The lack of significant difference between groups was evident for all components of the composite, as well as for all-cause death (16.7 percent vs 18.4 percent; HR, 0.90; p=0.13).

However, patients who received the influenza vaccine had a lower risk of all hospitalizations than placebo recipients (15.2 percent vs 17.1 percent; HR, 0.84, 95 percent CI, 0.74–0.97; p=0.01) as well as recurrent hospitalizations (21.8 percent vs 26.1 percent; HR, 0.83; p=0.001). Influenza vaccine recipients were also less likely to develop pneumonia than placebo recipients (2.4 percent vs 4.0 percent; HR, 0.58, 95 percent CI, 0.42–0.80; p=0.0006).

Benefits observed during peak flu season

The impact of influenza vaccination varied according to influenza period. For example, the risk of the primary outcome was reduced among vaccine vs placebo recipients during peak influenza periods (7.7 percent vs 9.4 percent; HR, 0.82, 95 percent CI, 0.68–0.99) but not during non-peak periods (7.5 percent vs 6.9 percent; HR, 1.08, 95 percent CI, 0.88–1.33).

The risks of all-cause death, CV death, or pneumonia were also lower among vaccine vs placebo recipients during peak influenza periods (all-cause death: 8.4 percent vs 10.6 percent; HR, 0.79; CV death: 6.7 percent vs 8.7 percent; HR, 0.77; pneumonia: 1.1 percent vs 2.1 percent; HR, 0.51). These reductions were not noted during non-peak influenza periods (all-cause death: 8.6 percent vs 8.1 percent; HR, 1.05; CV death: 6.6 percent vs 6.1 percent; HR, 1.07; pneumonia: 1.3 percent vs 2.0 percent; HR, 0.65).

“Many of the effects we found during peak flu circulation disappeared outside of it. There’s no biological explanation for that other than influenza infections,” Loeb noted.

Flu vaccine still a boon

According to Loeb, influenza increases the risk of CV events and deaths, and influenza vaccination has been tied to a lower rate of ischaemia-related CV events.

“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 HF,” he remarked.