Nationwide Utilization of Danish Government Electronic Letter System for Increasing InFLUenza Vaccine Uptake (NUDGE-FLU)

NUDGE-FLU was a nationwide, pragmatic, registry-based, cluster-randomized implementation trial during the 2022-23 influenza season in Denmark. NUDGE FLU randomized >960,000 Danish citizens aged 65 years or older to usual care or 9 different behaviorally informed electronic letters (9:1:1:1:1:1:1:1:1:1) promoting influenza vaccination. Letters explaining the potential cardiovascular benefits of influenza vaccination demonstrated a modest but significant improvement in vaccination uptake, a finding which was particularly pronounced in patients without vaccination in the prior influenza season, potentially indicating the ability to nudge a vaccine hesitant group.

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