A pooled analysis of three randomized controlled trials in Denmark shows that adult influenza vaccine uptake improved with electronic reminders emphasizing the vaccine's cardiovascular benefits -- particularly among those with a history of heart attack who weren't vaccinated the previous year.
A team led by Kaiser Permanente San Francisco researchers, which published the findings yesterday in JAMA Cardiology, said the low-cost, scalable intervention should be used to drive up flu vaccination in high-risk patients, such as those with cardiovascular disease (CVD).
"Influenza vaccination in patients with acute myocardial infarction (AMI) reduces major adverse cardiac events and is strongly recommended in clinical practice guidelines," the study authors wrote. "Effective strategies to improve vaccination are needed in these high-risk patients."
The three nationwide trials included in the analysis were conducted during the 2022-23 and 2023-24 flu seasons. The more than 2.1 million participants were randomly assigned to receive usual care or different behavior-based, emailed reminder letters, with the primary end point of flu vaccine receipt. The average age was 71.1 years, 51.9% were women, and 2.8% had a history of heart attack.
Usual care consisted of a standard communication letter from the Danish Health Authority with information on vaccine availability and appointment booking in two trials and no letter in the third.
Potential strategies for evaluation may include in-hospital, nursing-based vaccine administration, behavioral nudges embedded in cardiac catheterization reports, or novel treatment pathways.
All three studies demonstrated higher flu vaccination rates among heart attack survivors, who were more likely to have cardiac complications such as high blood pressure, rhythm abnormalities, and heart failure than those without.
Vaccine uptake rose modestly among all those sent a reminder letter compared with usual care -- regardless of heart attack status (+1.81 vs +1.32 percentage points). A letter that promoted the cardiovascular benefits of vaccination led to greater improvements among patients with a history of heart attack than among those without (+3.91 vs +2.03 percentage points).
And the greatest benefit was seen among heart attack survivors who didn't get vaccinated the year before (+13.7 vs +1.48 percentage points) and was also beneficial among younger participants who had a more recent heart attack.
In addition, a letter that prompted patients to commit to a vaccination time and place were more effective than usual care in heart attack survivors (3.04 vs 1.52 percentage points).
"Reasons behind gaps in vaccination rates among those with recent AMI are likely multifactorial," the researchers wrote. "First, this may reflect a risk-treatment paradox, in which patients at higher risk are less likely to be treated with disease-modifying therapies. In addition, there may be poor recognition of the broader benefits of vaccination outside of reducing respiratory infections."
In a news release from the American Heart Association, lead author Ankeet Bhatt, MD, MBA, of Kaiser Permanente, noted the need for more work. "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."
High-touch implementation strategies and cardiovascular-focused messaging may be needed to more directly connect vaccination to CVD events, the authors said.
"Potential strategies for evaluation may include in-hospital, nursing-based vaccine administration, behavioral nudges embedded in cardiac catheterization reports, or novel treatment pathways, including vaccination administration during or just after coronary angiogram (eg, at the time of antiplatelet loading)," they concluded.
In a related commentary, Mohammad Madjid, MD, of the University of California Los Angeles, and Payam Safavi-Naeini, MD, MPH, of the Texas Heart Institute, noted suboptimal flu vaccination rates among patients with CVD and only modest progress (a 1.1% increase) in the past 10 years.
"As of 2020, only 44.3% of adults with CVD received the influenza vaccine, far short of the 70% goal set by the Healthy People 2020 initiative," they wrote. "After failing to reach the 70% target in 2020, Healthy People 2030 has set the new goal of a 70% vaccination rate for US adults by 2030."
Beyond economic and access issues, the experience of suboptimal acceptance of the COVID-19 vaccine despite its free accessibility in the US underscores the complexity of the approach to vaccination and highlights the impact of social media misinformation and other sources of vaccine hesitancy.
But Madjid and Safavi-Naeini warned against generalizing the study results to the US population, which has much lower baseline flu vaccination rates than those in Danish adults. In Denmark, uptake neared 80% in people aged 18 to 64 years with a recent heart attack (two studies) and was 65% in the third study.
In contrast, flu vaccine coverage is about 33.3% in US adults aged 18 to 44 years and 48% in those aged 45 to 64 with CVD.
"This discrepancy may be attributed to several factors, including access to universal health care, free vaccinations in Denmark, and longstanding public health initiatives that have raised health awareness over time," they wrote. "Beyond economic and access issues, the experience of suboptimal acceptance of the COVID-19 vaccine despite its free accessibility in the US underscores the complexity of the approach to vaccination and highlights the impact of social media misinformation and other sources of vaccine hesitancy."
The intervention of private and governmental sectors, including healthcare professionals, in the United States is crucial to improving flu vaccine uptake and reducing racial disparities among CVD patients, the commentary authors said. "For the 2021 to 2022 influenza season, the adult vaccination rate was 54% for White individuals, compared with 41% for American Indian or Alaska Native individuals, 42% for Black individuals, and 38% for Hispanic individuals."
They urge using a combination of electronic reminders, individual counseling, financial incentives, and strong provider recommendations to boost uptake.
Artificial intelligence models "could identify patients at the highest risk of complications from influenza, particularly those with a cardiac history, and generate personalized, behaviorally informed nudges," Madjid and Safavi-Naeini concluded. "These messages could address individual patient barriers and hesitations and provide targeted educational content to enhance vaccination uptake."