In the American College of Cardiology (ACC) 2022 Scientific Session, Professor Mark Loeb from McMaster University, Canada, discussed his randomized controlled trial of influenza vaccines in heart failure (HF) patients to reduce adverse vascular events.¹

The risk of cardiovascular (CV) events and death increases among patients infected with influenza virus, but a lower rate of CV events has been reported with flu vaccines.¹ The low- and middle-income countries appear to have the highest CV disease burden due to their lower influenza vaccination rates.¹ Therefore, this pragmatic multinational trial was conducted to examine the role of inactivated influenza vaccine in preventing the CV outcomes when compared with placebo.¹

Adult patients who have HF with the New York Heart Association (NYHA) functional class II, III, IV were included, and inactivated influenza vaccines (VAXIGRIP, trivalent or quadrivalent inactivated vaccines) were administered intramuscularly at a dose of 0.5mL annually for 3 influenza seasons.¹ The primary endpoints were the composite of CV death, non-fatal myocardial infarction (MI) and non-fatal stroke, while the composite endpoint was

hospitalizations for HF.¹ The key secondary endpoints included components of the primary endpoints, all hospitalizations, pneumonia, and all deaths.¹

The baseline characteristics showed a number of well-balanced groups with the inclusion of patients from different countries with a median age of 57 years.¹ Most patients belonged to the NYHA class II and/or had severe left ventricular function (ejection fraction ≤30%).¹ Moreover, comorbidities, such as hypertension, stroke, MI, or diabetes, and the use of medications such as beta-blockers, angiotensin-converting enzyme inhibitors (ACEIs) or angiotensin II receptor blockers (ARBs), diuretics, and antiplatelets, were common among these patients. ¹ The first and second primary outcomes occurred in 14.8% and 20.3% of the intervention group, respectively; and in 16% and 22.1% of the placebo group, respectively. ¹ However, the results observed were not statistically significant. ¹ In contrast, analysis of the secondary endpoints demonstrated a significant reduction in all hospitalizations (HR=0.84; 95% CI: 0.74-0.97; p<0.01), pneumonia (HR=0.58; 95% CI: 0.42-0.8, p<0.0006), and recurrent events for all hospitalizations (HR=0.83; 95% CI: 0.74-0.93; p<0.001). ¹ An 18% of risk reduction in influenza events was detected during the peak influenza season, but this effect was not significant outside the peak season. ¹ Similarly, all deaths and CV deaths were only significant during the peak influenza season. ¹

In conclusion, influenza vaccine did not lead to a significant decrease in the risk of CV death, non-fatal MI, and non-fatal stroke compared with placebo, except during the peak influenza season. ¹ Nevertheless, it reduced the risk of pneumonia and hospitalizations in the vaccinated group. ¹