Background Catch-up HPV vaccination is challenging in many low and middle-income countries (LMICs). Pay-it-forward offers an individual a subsidized vaccine, then an opportunity to donate to help others access vaccinations. Our randomized control trial assessed the effectiveness of pay-it-forward in improving HPV vaccination among girls aged 15-18 years in China.

Methods and findings Eligible participants were randomly assigned to either the pay-it-forward arm or standard-of-care arm (self-paid vaccination). The primary outcome was the first-dose HPV vaccination rate, verified against clinical records. Among 321 participants enrolled, most caregivers were female (80.1%). In the pay-it-forward arm, 55 of 161 (34.2%) girls received the HPV vaccine, compared with 28 of 160 (17.5%) girls in the standard-of-care arm (adjusted proportion difference = 17.9%, 95% CI: 8.7, 27.0, P<0.001). Among 55 girls in the pay-it-forward arm who received the vaccination, 37 (67.3%) wrote a postcard message, and 39 (70.9%) of their caregivers donated to support future girls. The financial cost per person vaccinated was $294 in the standard-of-care arm and $230 in the pay-it-forward arm.

Conclusions The pro-social pay-it-forward strategy was effective to increase catch-up HPV vaccination among teenage girls with comparable costs.

Trial Registration ChiCTR2200055542

The authors have declared no competing interest.

ChiCTR2200055542

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The Ethics Committee of West China Fourth Hospital and West China School of Public Health approved the study.(Gwll2021057/ Gwll2023125).

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