Pay-it-forward to improve influenza vaccine uptake and public engagement among children and older adults in China

China has low seasonal influenza vaccination rates among children and older adults. This quasi-experimental pragmatic trial examined the effectiveness of a pay-it-forward intervention on influenza vaccine uptake compared to standard of care (user-paid vaccination) and free vaccination strategies among children and older people in China (ChiCTR2000040048). In pay-it-forward, people receive a free influenza vaccine from a local group and are then asked if they would like to donate financially to promote vaccination among future individuals. Among 450 participants enrolled, 55/150 (36.7%) in the standard of care arm, 111/150 (74.0%) in the pay-it-forward arm, and 114/150 (76.0%) in the free vaccination arm received an influenza vaccine. Similar trends were observed among children and older adults. The pay-it-forward arm had significantly higher vaccine confidence when compared to the standard of care arm. In the pay-it-forward arm, 107/111 (96.4%) of participants donated money for subsequent vaccinations and 19 of 60 invited (31.7%) created postcard messages.