Introduction
Influenza remains a significant health challenge worldwide, particularly for individuals with chronic illnesses and cardiovascular disease (CVD), where the risks of severe complications are substantially higher. Despite strong recommendations from health authorities advocating influenza vaccination as a preventive measure, vaccination rates among younger and middle-aged adults with chronic conditions often fall short of optimal levels. Recent research has focused on leveraging digital nudges—behaviorally informed electronic communications—to enhance vaccine uptake in these vulnerable populations. This article synthesizes findings from multiple large-scale randomized clinical trials conducted in Denmark, evaluating the efficacy and clinical impacts of digitally delivered nudges to increase influenza vaccination among patients with chronic diseases, including those with a history of acute myocardial infarction (AMI).
Behaviorally Informed Electronic Letters to Increase Vaccination in Chronic Disease Patients
Two major nationwide, registry-based randomized clinical trials (RCTs) investigated the effectiveness of digital nudges in Danish citizens aged 18 to 64 years who were eligible for free influenza vaccination due to chronic diseases. Participants were randomized to receive usual care (no letter) or one of six behaviorally designed electronic letter strategies.
Findings consistently demonstrated that any form of intervention letter significantly improved influenza vaccination rates compared with usual care. For example, one trial found a 12.4 percentage point increase (36.5% vs. 24.1%) in vaccination uptake among those receiving any letter. Notably, letters focusing on the cardiovascular benefits of vaccination and those sent as repeated reminders showed the largest effects, with increases up to 15 percentage points. Importantly, these improvements were evident even among participants who had received similar nudges in the prior influenza season, suggesting sustained effectiveness over multiple years.
The second trial corroborated these results, with an overall 11.7 percentage point increase in vaccination rates in the intervention group (39.6% vs. 27.9%). The most effective nudges included a follow-up letter sent 10 days after the initial contact and those emphasizing cardiovascular health gains attributable to vaccination. These effects were consistent across major demographic and clinical subgroups.
Targeted Nudges in Patients With a History of Myocardial Infarction
Patients with AMI represent a particularly high-risk group, as influenza vaccination reduces risks for major adverse cardiac events. A pooled meta-analysis of three nationwide RCTs focusing on adults with chronic disease and specifically those who had experienced an AMI provided critical insights.
Overall improvements in vaccination uptake were similar between patients with and without AMI history when considering all nudges combined. However, letters explicitly highlighting the cardiovascular benefits of vaccination yielded significantly higher increases in vaccine acceptance in AMI patients compared to those without such history (3.91 vs. 2.03 percentage points). This beneficial effect was especially pronounced in AMI patients who were unvaccinated in the previous season and in younger patients with more recent infarctions.
These findings underscore the value of tailored messaging that communicates direct health benefits relevant to the patient’s condition, enhancing motivation and uptake.
Clinical Outcomes Associated With Digital Nudges
A prespecified exploratory analysis of a randomized implementation trial involving Danish citizens aged 65 years or older assessed whether increased vaccination due to electronic nudges translated into measurable clinical benefits. Despite modest improvements in vaccination rates, no statistically significant reduction was observed in hospitalizations for pneumonia or influenza, all-cause hospitalizations, or mortality within the follow-up period.
Several factors may contribute to these findings, including limitations inherent in observational registry data, the relatively short follow-up duration, and the relatively small absolute increases in vaccination coverage. The authors caution that these results do not diminish the importance of influenza vaccination but highlight the complexity in demonstrating clinical outcome benefits in pragmatic population studies.
Implications for Practice and Public Health
The aggregation of evidence from these rigorously conducted nationwide RCTs supports digital nudging via electronic letters as an effective, scalable, and low-cost strategy to increase influenza vaccination rates in patients with chronic diseases and CVD, including high-risk post-AMI individuals.
Key practical takeaways include:
– Repeated communications and content emphasizing specific cardiovascular benefits maximize impact.
– Digital nudges are effective across diverse patient subgroups and can sustain improved vaccination behavior across seasons.
– Integration of behavioral science principles enhances intervention design and effectiveness.
Healthcare systems and policymakers should consider incorporating digital behavioral economic strategies within existing vaccination programs to improve coverage, reduce the burden of influenza-related morbidity, and potentially improve cardiovascular health outcomes in vulnerable populations.
Conclusion
Electronic delivery of behaviorally informed nudges significantly improves influenza vaccination uptake among patients with chronic and cardiovascular diseases. Emphasizing cardiovascular benefits and sending repeated letters are particularly effective approaches. While improvements in vaccination rates are clear, the translation into direct measurable clinical outcomes requires further long-term evaluation. Nonetheless, these interventions represent promising tools for enhancing public health efforts to protect high-risk patients from influenza complications.
References
Johansen ND, Vaduganathan M, Bhatt AS, et al. Digital Nudges to Increase Influenza Vaccination in Patients with Chronic Diseases. NEJM Evid. 2026;5(1):EVIDoa2500265.
Johansen ND, Vaduganathan M, Bhatt AS, et al. Electronic Nudges to Increase Influenza Vaccination in Patients With Chronic Diseases: A Randomized Clinical Trial. JAMA. 2024;332(22):1900-1911.
Bhatt AS, Johansen ND, Vaduganathan M, et al. Electronic Nudges and Influenza Vaccination Among Patients With a History of Myocardial Infarction: Insights From 3 Nationwide Randomized Clinical Trials. JAMA Cardiol. 2025;10(1):78-86.
Johansen ND, Vaduganathan M, Bhatt AS, et al. Clinical Outcomes With Electronic Nudges to Increase Influenza Vaccination: A Prespecified Analysis of a Nationwide, Pragmatic, Registry-Based, Randomized Implementation Trial. Ann Intern Med. 2024;177(4):476-483.
