Abstract
BACKGROUND: Despite evidence demonstrating that influenza vaccination is associated with reduced risk of cardiovascular events and all-cause mortality in individuals with diabetes mellitus (DM), vaccine uptake remains suboptimal. OBJECTIVES: The purpose of this study was to assess the effectiveness of electronically delivered nudges on influenza vaccine uptake according to the presence of DM status versus other chronic diseases. METHODS: NUDGE-FLU-CHRONIC was a nationwide, randomized, pragmatic implementation trial among younger and middle-aged (18-64 years) Danish citizens with chronic disease during the 2023/2024 influenza season. Participants were randomized in a 2.45:1:1:1:1:1:1 ratio to usual care (no electronic letter) or 1 of 6 different electronic nudge letters. The endpoint was receipt of a seasonal influenza vaccine on or before January 1, 2024. RESULTS: Of 299,881 participants, 57,666 (19.2%) had DM (median age: 51.6 years, 43.0% female). During the season, 43.0% of those with DM vs 34.6% of those without DM received the vaccine (P < 0.001). Any electronic letter vs usual care was highly effective in increasing vaccine uptake in participants with DM (45.6% vs 36.5%, difference: +9.1 percentage points [99.29% CI: 7.9-10.3], relative risk ratio: 1.42 [99.29% CI: 1.39-1.44]). However, DM status modified the effect of the interventions such that participants without DM at baseline experienced a greater relative gain than those with DM (37.3% vs 25.9%, difference: +12.3 percentage points [99.29% CI: 11.7-12.8], risk ratio: 1.47 [99.29% CI: 1.45-1.50]; P (interaction)<0.001). CONCLUSIONS: Electronic nudge letters effectively boosted vaccine uptake in individuals with DM and in individuals free of DM but with other chronic diseases, but the effect was lower among those with DM. Electronic nudges represent a low-cost and effective strategy to boost influenza vaccination rates in the DM population. (Nationwide Utilization of Danish Government Electronic Letter System for Increasing InFLUenza Vaccine Uptake Among Adults With Chronic Disease; NCT06030739).