Electronic nudges boost flu vaccination rates among heart attack survivors

An electronic letter, or nudge, highlighting the cardiovascular benefits of influenza vaccines improved vaccination rates among more than 2 million adults—with a greater impact on those who have had a heart attack—across three clinical trials spanning the most-recent, two consecutive influenza seasons in Denmark. This was the finding of late-breaking science presented today at the American Heart Association's Scientific Sessions 2024. The meeting, Nov. 16-18, 2024, in Chicago, is a premier global exchange of the latest scientific advancements, research and evidence-based clinical practice updates in cardiovascular science. This research is simultaneously published today Journal of the American Medical Association - Cardiology (JAMA Cardiology).

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, with rare exceptions. Influenza vaccination, also known as a flu shot, is critical in preventing the flu and its related complications. In addition to its effects on preventing infection, routine flu vaccination has also been shown to reduce major cardiovascular health problems in people with a prior heart attack.

Yearly influenza vaccines help prevent influenza infection and, in patients with a heart attack, are potentially cardioprotective. However, there are large gaps in implementing this effective therapy, and novel, scalable strategies to improve flu vaccination rates are needed."

Ankeet Bhatt, M.D., M.B.A., Sc.M., study's lead author, cardiologist at Kaiser Permanente San Francisco Medical Center, research scientist at the Kaiser Permanente Northern California Division of Research, and adjunct professor at the Stanford University School of Medicine in Palo Alto, California

In Denmark, about 80% of older adults get flu shots, while only about 40% of younger adults with chronic diseases get flu shots, Bhatt added.

In the U.S., 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.

To identify which outreach methods might help increase how many people get the flu vaccine, the study authors evaluated whether electronic letter-based reminders would improve vaccine use in a broad population including older adults and those with chronic medical disease during two recent flu seasons in Denmark.

The researchers conducted three national clinical trials: NUDGE-FLU; NUDGE-FLU-2; and NUDGE-FLU CHRONIC during the 2022-2023 and 2023-2024 flu seasons. Each trial assessed a series of behavioral science-informed nudges, delivered via a governmental electronic email/letter system. Participants were selected randomly to receive one of the email letters encouraging flu vaccination or no email reminder/standard of care. An electronic letter explaining the potential cardiovascular benefits of flu shots was more effective at increasing vaccination rates.

The study found:

• Compared to usual care, people who received any of the nudge email letters had higher rates of vaccination: an improvement of 1.8% among heart attack survivors and an increase of 1.3% among adults without a history of heart attack.
• A message that explained the potential cardiovascular benefits of flu shots was more effective, leading to a 3.9% increase in vaccination among people with a history of heart attack compared to a 2% increase for those with no heart attack history.
• Among heart attack survivors, an email focused on cardiovascular benefits was even more successful among those who were not vaccinated in the previous flu season. People in this subcategory had a flu vaccine improvement rate of nearly 14% compared to an improvement in heart attack survivors who were previously vaccinated of only about 1.5%.
• 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, 26% increase vs. 14% increase, respectively. "These particularly important groups, those not previously vaccinated and those with a recent heart attack, may represent groups with the greatest cardiovascular protection to gain from vaccination," Bhatt said.

"The data suggest that cardiovascular focused messaging was effective across a broad population; this strategy should be considered as part of a suite of strategies to improve cardiovascular prevention and encourage flu vaccination among high-risk patients, including those with a history of heart attack," Bhatt said. "Notably, this strategy alone did not close all implementation gaps for flu vaccination. Other strategies in addition to messaging-based intervention need to be tested to fully close this important prevention gap in at-risk patients."

Given the encouraging results across this large population over two recent flu seasons, this low-cost, scalable strategy, particularly if validated in other global healthcare contexts, should be considered for population-level outreach globally to improve flu vaccination rates across health care systems and countries, he said.

A limitation of the research is that it's based on a prespecified, secondary analysis across the trials, meaning the studies were not solely dedicated to answering this question alone. In addition, especially among older adults, 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, Bhatt said.

Study details, background and design:

• 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.