In a recent study published in The Lancet Global Health, researchers conducted a placebo-controlled, double-blind clinical trial to assess whether influenza vaccination effectively reduced vascular events and mortality among patients with heart failure.
Heart failure is a major global health concern, and the incidence of heart failure has doubled in the last three decades. Furthermore, influenza infections have increased the risk of cardiovascular incidents and death.
However, observational studies, placebo-controlled trials, and cohort studies have reported a decrease in ischemic events and all-cause mortality in patients with a history of cardiovascular conditions. Given the low influenza vaccination rates and increased risk of heart failure in low- and middle-income countries, it would be helpful to understand the effectiveness of the influenza vaccination in reducing the risk of cardiovascular events in patients with a history of heart failure.
About the study
In the present study, the researchers conducted a randomized, placebo-controlled clinical trial in 30 locations in 10 countries in Africa, Asia, and the Middle East. The trial compared the effect of the influenza vaccination and a placebo on the incidence of cardiovascular events in heart failure patients over three influenza seasons. The locations consisted of hospitals associated with research institutes or universities, and the patients with heart failure were recruited from the hospitals or using local health databases.
Patients above 18 with clinically diagnosed heart failure were recruited for the study. Participants were excluded from the study if they presented any contraindications to the vaccine or had received the influenza vaccine in the last three years. Patients with a severe valvular disease requiring surgeries to repair or replace heart valves were also excluded.
The participants were randomly assigned to the vaccination or placebo group in a 1:1 ratio and intramuscularly administered 0.5 ml of the influenza vaccine or saline, respectively. The primary outcomes included non-fatal myocardial infarction, hospitalizations related to heart failure, non-fatal stroke, and cardiovascular deaths. The secondary outcomes included all primary outcomes, all-cause death, all-cause hospitalization, and pneumonia.
The results reported a significant decrease in primary and secondary outcomes among patients in the vaccination group during peak influenza season. However, the results were not statistically significant for the entire observation period.
A total of 5,129 patients were enrolled in the study, with 2,560 receiving the influenza vaccine and the rest receiving the placebo. Primary outcomes such as cardiovascular death, non-fatal stroke, and myocardial infarction occurred in 380 and 410 participants from the vaccination and placebo groups, respectively. When hospitalization for heart failure was added to the outcomes, the numbers increased to 524 and 570 for the vaccination and placebo groups, respectively. Furthermore, when the recurrent events were analyzed, the incidence of cardiovascular death, non-fatal stroke or myocardial infarction, and hospitalization for heart failure increased to 754 and 819 for the vaccination and placebo groups, respectively.
Secondary outcomes of pneumonia and all-cause hospitalizations were observed to be significantly lower among patients in the vaccination group as compared to those in the placebo group. However, the other secondary outcomes, such as cardiovascular death, all-cause death, hospitalization for heart failure, and non-fatal stroke, and myocardial infarction did not show any significant decrease in either of the two groups.
However, during peak influenza circulation periods, the primary and secondary outcomes were significantly reduced in the vaccination group compared to the placebo group. Furthermore, the events were also lower when the vaccine strain was similar to the circulating influenza strain.
The reduction in risk during peak influenza season seen in the present study was similar to another study that investigated the effectiveness of the influenza vaccine in reducing all-cause death and myocardial infarction in patients with a history of myocardial infarction. The results also corroborated the findings of the meta-analysis of other observational studies on the effect of the influenza vaccine in reducing cardiovascular events in heart failure patients.
Overall, the findings reported that administration of the influenza vaccine resulted in a significant decrease in cardiovascular death, hospitalizations related to heart failure, non-fatal stroke, and non-fatal myocardial infarctions in patients with a history of heart failure during peak periods of influenza virus circulation.
Although the risk reduction was not significant for the overall observation period, the significant decrease in cardiovascular events and death and the marked reduction in pneumonia associated with influenza vaccination during peak virus circulation periods suggest a clinical benefit to administering the vaccine.