Clinical Outcomes With Electronic Nudges to Increase Influenza Vaccination: A Prespecified Analysis of a Nationwide, Pragmatic, Registry-Based, Randomized Implementation Trial: Annals of Internal Medicine: Vol 0, No 0
Background: In the NUDGE-FLU (Nationwide Utilization of Danish Government Electronic letter system for increasing inFLUenza vaccine uptake) trial, electronic letters incorporating cardiovascular (CV) gain-framing and repeated messaging increased influenza vaccination by approximately 1 percentage point. Objective: To evaluate the effects of the successful nudging interventions on downstream clinical outcomes. Design: Prespecified exploratory analysis of a nationwide randomized implementation trial. (ClinicalTrials.gov: NCT05542004) Setting: The 2022 to 2023 influenza season. Participants: 964 870 Danish citizens aged 65 years or older. Intervention: Usual care or 9 different electronically delivered behavioral nudging letters. Measurements: Cardiovascular, respiratory, and other clinical end points during follow-up from intervention delivery (16 September 2022) through 31 May 2023. Results: The analysis set included 691 820 participants. Hospitalization for pneumonia or influenza occur