A cluster randomised trial of digital messaging nudges to improve influenza vaccination uptake in China

As an effective strategy for preventing influenza, vaccination uptake remains suboptimal. This cluster randomised trial evaluated digital messaging nudges on influenza vaccination among children aged 6-35 months and their parents in China. During 2024-25 flu season, 36 community health centres were randomly assigned to one of six arms by message framing (gain vs. loss) and evidence type (statistical vs. narrative), and standard message and no-message control, with 2,011 parents of age-eligible children enroled. For childhood vaccination, loss-framed narrative arm achieved the highest uptake (24.0% vs. control 9.4%; adjusted RR 2.50, 95% CI 1.27-4.94), and effects sustained at five-month follow-up. Loss-framed statistical arm (16.9% vaccination uptake) was significantly effective only at one-month follow-up (RR 2.73; 95% CI 1.50-4.99), with effects attenuating rapidly. Both standard and gain-framed messages had no significant effect on childhood vaccination. Loss-framed narrative digital nudges offer a scalable strategy to improve childhood vaccination. Clinical trial registration: ChiCTR2400092213.