Family Physician Nudges for Influenza Vaccination Among Older Adults

The goal of this clinical trial is to learn if a family-physician nudge intervention works to improve influenza vaccination among adults aged 55 years and older in China. Three independent, parallel cluster randomized controlled trials will be conducted under three distinct vaccine payment policies, i.e. free vaccination for those older than 65 years and self-paid vaccination for those \<65 years in rural areas, and partially insurance-covered vaccination in urban areas.

The main questions it aims to answer are:

1. Does the family-physician nudge intervention increase influenza vaccination uptake among older adults? How does the effectiveness of the nudge intervention vary under different payment policies？ 2. Is the family-physician nudge intervention cost-effective, acceptable, feasible, and potentially sustainable in primary care settings? Researchers will compare an intervention group receiving a family-physician nudge with a control group receiving routine care to see if the nudge is effective at increasing influenza vaccination among older adults.

Participants will:

1. Be recruited at community health service centers and cluster-randomized by their family physicians into one of two groups. 2. Receive either a physician nudge (provider recommendation by an endowment-framing educational pamphlet + default appointment + a follow-up reminder) or routine health education. 3. Have their influenza vaccination status verified through the immunization information system at the end of the trial.