In a scenario marked by the progressive decline in vaccination coverage and the spread of campaigns that sow doubt about vaccine safety, protecting vulnerable groups has become an even more urgent challenge. Adults, especially those with chronic diseases, remain below optimal influenza vaccination coverage, revealing gaps in prevention. Digital interventions inspired by behavioral science, so-called electronic nudges, are scalable strategies to overcome adherence barriers. This systematic review and meta-analysis assessed the effectiveness of nudges in increasing vaccination coverage among adults in the general population and in three priority subgroups: immunosuppressed individuals, those with chronic cardiovascular disease, and people with diabetes. Following the PRISMA checklist and with a protocol registered in PROSPERO, we searched PubMed/MEDLINE, Cochrane CENTRAL and Embase up to June 2025. Of 1,064 records identified, 230 duplicates and 834 abstracts were removed; 18 full-text articles were assessed, and eight randomized clinical trials (RCTs) met the inclusion criteria. We included RCTs comparing digital messages (SMS, email, electronic letter or portal) versus no notification. The primary outcome was the proportion of the population vaccinated. Odds ratios (ORs) were pooled using the Mantel–Haenszel method (fixed effect), and heterogeneity was measured using I²; a random-effects model was used in sensitivity analyses. Eight RCTs (total N = 1,289,382 participants) met the inclusion criteria. In the general population, nudges significantly increased vaccination uptake (OR 1.16; 95% CI 1.15–1.17; I² = 100%). The effect was greater in immunosuppressed individuals (OR 1.56; 95% CI 1.49–1.62; I² = 98%), substantial in those with chronic cardiovascular disease (OR 1.40; 95% CI 1.36–1.44; I² = 99%), and modest in people with diabetes (OR 1.17; 95% CI 1.14–1.20; I² = 96%). Sensitivity analyses did not change the direction of the results, although one study contributed significantly to the high heterogeneity. No publication bias was detected. Electronic nudges increase influenza vaccination rates in adults, with the greatest benefit/adherence observed among immunocompromised individuals. Their routine implementation in health systems and public portals may accelerate coverage targets with the potential to reduce seasonal morbidity and mortality. Future studies should standardize outcomes and explore personalized message formats.
Zonta et al. (2026) studied this question.