Electronic nudges to increase influenza vaccination uptake in younger and middle-aged individuals with atrial fibrillation: a prespecified analysis of the NUDGE-FLU-CHRONIC trial

Aims Little is known regarding strategies to improve influenza vaccination uptake among individuals with atrial fibrillation (AF). We assessed the effect of electronically delivered behavioural nudges on influenza vaccination uptake and clinical outcomes according to AF status. Methods and results This is a prespecified analysis of the nationwide randomized NUDGE-FLU-CHRONIC trial in which citizens aged 18-64 years with a chronic disease were randomized to usual care or six different electronic nudge letters aiming to increase influenza vaccination uptake during the 2023-2024 influenza season. The primary endpoint was receipt of an influenza vaccine on or before 1 January 2024. We reported absolute differences and relative risks (RRs) of each intervention letter vs. usual care on influenza vaccination uptake and assessed effect modification by AF status using binomial regression. Among 299 881 randomized participants, 19 481 (6.5%) had a history of AF (median age 58.5 years, 27.8% female). During follow-up, 41.5% of participants with a history of AF received influenza vaccination compared with 35.8% of those without (P < 0.001). In the overall population, influenza vaccination uptake was higher among those receiving any electronic nudge letter compared with usual care. AF status modified the absolute effect of any electronic letter on influenza vaccination uptake (P interaction < 0.001): the effect of any electronic letter was higher among those who had a history of AF [45.9 vs. 31.1%; difference: +14.8% points; 99.29% confidence interval (CI) (12.8-16.8), RR: 1.48, 99.29% CI (1.39-1.56)] compared with those without AF [39.1 vs. 27.7%; difference: +11.4% points; 99.29% CI (10.9-12.0), RR: 1.41, 99.29% CI (1.39-1.44)]. Similar results were observed for the individual electronic letter-based nudges. Conclusion In this prespecified, secondary analysis, electronic nudge letters highlighting the importance of influenza vaccination were especially effective in increasing influenza vaccination uptake among young and middle-aged adults with AF, supporting simple electronic letters as an efficient public health strategy to improve vaccination coverage in high-risk groups.