Flu Shot Reminders Improve Use in Heart Attack Survivors

An electronic nudge explaining the cardiovascular benefits of the influenza vaccine increased vaccination rates, particularly among people who had previously had a heart attack, showed the NUDGE FLU series of clinical trials.

Influenza has the potential to be a dangerous infection on its own, but it increases the risk for cardiovascular events among people with a history of heart attack, said the study’s lead author, Ankeet Bhatt, MD, a cardiologist at Kaiser Permanente San Francisco Medical Center, San Francisco.

“Yearly influenza vaccines help prevent influenza infection and, in patients with a heart attack, are potentially cardioprotective,” he said during his presentation at the American Heart Association (AHA) Scientific Sessions 2024 in Chicago. The NUDGE FLU results were simultaneously published online in JAMA Cardiology.

In Denmark, where the trials were conducted, about 80% of older adults get flu shots, but only about 40% of younger adults with chronic diseases do, Bhatt reported. In the United States, about 45% of adults and 55% of children received at least one dose of the flu vaccine in the 2023/24 flu season, according to the US Centers for Disease Control and Prevention (CDC).

The NUDGE FLU Trials

Bhatt and his colleagues conducted three related clinical trials during the 2022/23 and 2023/24 flu seasons: NUDGE-FLU and NUDGE-FLU-2 targeted older adults, whereas NUDGE-FLU-CHRONIC targeted younger adults with chronic diseases. Nearly 2 million people were involved in the three trials.

Participants were randomized to receive one of a series of different behavioral-science-informed letters, delivered through a government-run electronic communication system, or no reminder.

People who received any of the nudges had higher rates of vaccination; among heart attack survivors, there was a 1.8% improvement and among adults without a history of heart attack, there was a 1.3% improvement. But a nudge that explained the potential cardiovascular benefits of flu shots was even more effective, leading to a 3.9% increase among people with a history of heart attack and a 2% increase among those with no heart attack history.

“A simple sentence resulted in a durable improvement in the vaccination rate,” said Bhatt.

The effect was even greater among those who had not been vaccinated in the previous flu season. Among heart attack survivors, nearly 14% more people got the vaccine compared with just 1.5% more survivors who were previously vaccinated. And it was most effective among younger adults who had experienced a recent heart attack, resulting in a 26% increase.

“The impact was larger in patients with a history of acute myocardial infarction, in those who were vaccine-hesitant, and in younger people” — all groups with the most to gain from vaccination in terms of cardiovascular protection — Bhatt reported.

About 25% of people in the United States are unsure about whether to get a flu shot, said Orly Vardeny, PharmD, professor of medicine at the University of Minnesota Medical School in Minneapolis, who was not involved in the study. The fact that previously unvaccinated people were convinced by the nudges is reassuring. “That’s the group where this intervention is most likely to move the needle,” she said.

Around half of all people hospitalized for flu in the United States have cardiovascular disease, CDC data showed, so “even a small increase in the number of patients who get vaccinated has substantial public health benefits,” Vardeny said.

The NUDGE FLU series showed that nudges like this should be employed as a simple tool to improve vaccination rates, but the system would be much more difficult to implement in the United States, Bhatt said.

Denmark has a national health service and a preexisting government electronic communication system, whereas the US system is privately run and more fractured. It would be possible to make it work, he pointed out, but would take some effort.