An electronic message intervention, designed to encourage flu vaccination by highlighting its cardiovascular benefits, has demonstrated a significant improvement in vaccination rates among adults in Denmark, particularly benefiting those with a history of heart attack. The findings, presented at the American Heart Association’s Scientific Sessions 2024 and published in the Journal of the American Medical Association – Cardiology (JAMA Cardiology), suggest that this low-cost, scalable strategy could be implemented globally to improve vaccination rates.
The study, led by Ankeet Bhatt, M.D., M.B.A., Sc.M., a cardiologist at Kaiser Permanente San Francisco Medical Center, involved over 2 million adults across three clinical trials (NUDGE-FLU, NUDGE-FLU-2, and NUDGE-FLU CHRONIC) during the 2022-2023 and 2023-2024 flu seasons. Participants were randomized to receive an email letter promoting flu vaccination or to a standard of care group without the reminder.
The results indicated that individuals who received the email reminders had higher vaccination rates compared to the usual care group. Specifically, there was a 1.8% improvement in vaccination rates among heart attack survivors and a 1.3% increase among adults without a history of heart attack. The most effective message, which emphasized the cardiovascular benefits of flu shots, led to a 3.9% increase in vaccination among people with a history of heart attack, compared to a 2% increase for those without such history.
Impact on Previously Unvaccinated Individuals
Notably, the intervention had the most significant impact on heart attack survivors who were not vaccinated in the previous flu season. This subgroup experienced a flu vaccine improvement rate of nearly 14%, compared to an improvement of only about 1.5% in previously vaccinated heart attack survivors. In one of the trials (NUDGE-FLU-CHRONIC), the nudge highlighting cardiovascular benefits was even more effective among younger adults with a recent heart attack, showing a 26% increase versus a 14% increase, respectively.
Clinical Significance
"Yearly influenza vaccines help prevent influenza infection and, in patients with a heart attack, are potentially cardioprotective," said Dr. Bhatt. "However, there are large gaps in implementing this effective therapy, and novel, scalable strategies to improve flu vaccination rates are needed."
The American Heart Association and the U.S. Centers for Disease Control and Prevention (CDC) recommend annual flu vaccination for nearly all people ages 6 months and older, including those with heart disease. Despite these recommendations, vaccination rates remain suboptimal. For example, in the U.S. during the 2023-2024 flu season, about 45% of adults and 55% of children received at least one dose of the flu vaccine, according to the CDC.
Study Limitations and Future Directions
Dr. Bhatt noted that a limitation of the research is that it’s based on a prespecified, secondary analysis across the trials. Also, flu vaccination rates in Denmark were high; vaccination rates may be much lower in other parts of the world. Whether that changes the effectiveness of this strategy in populations with lower vaccination rates requires further study, and validation efforts are already under way in the United States.
Study Details
The clinical trials included more than 2 million adults, ages 18-64 years-old. More than 59,450 participants had a history of heart attack: 11,760 in the NUDGE-FLU CHRONIC trial, and more than 47,690 in the NUDGE-FLU and NUDGE-FLU 2 trials combined. Among those with a history of heart attack, the average age across the three trials was 70 years old, and 28% were women.
