BackgroundChina has low human papillomavirus(HPV) vaccination rate due to lack of public funding and mistrust in domestic vaccines. This pilot study evaluated the feasibility and preliminary effectiveness of an innovative pay-it-forward strategy, which has a participant receive a subsidized vaccine and offers her an opportunity to donate to support other girls, in improving HPV vaccine uptake among 15–18-year-old adolescent girls.MethodsA two-arm randomized controlled pilot trial was performed in one vaccination clinic in Western China. Adolescent girls (via caregivers) were invited to participate the study via online dissemination of the pilot study. Eligible ones were then randomly allocated using a sealed envelope method into standard-of-care or pay-it-forward arm in a 1:1 ratio. Pay-it-forward participants received hand-written postcard messages, a subsidized vaccine, and an opportunity to donate and (or) write postcards for future recipient girls. Standard-of-care participants self-paid for vaccines. The primary outcome was the first-dose HPV vaccine uptake, which was calculated using multivariable logistic regression, presented as crude/adjusted odds ratios (cORs/aORs) and 95% con dence intervals (CIs). Standard scales were used to assess the feasibility of the program.ResultsA total of 100 participants (50 in each arm) were recruited from Jan 4, 2022 to Feb 18, 2022. The HPV vaccine uptake rate was 98% (49/50) in the pay-it-forward arm and 82% (41/50) in the standard-of-care arm (cOR = 10.76, 95%CI: 1.31–88.47,P= 0.027; aOR= 12.12, 95%CI: 1.37–107.29,P= 0.025). The completion rate of full schedule of HPV vaccination in the two arms was 100% (49/49) and 95.1% (39/41), respectively. Of all 49 vaccinated girls in the pay-it-forward arm, 38 (77.6%) donated to support future participants, and the total donation accounted for 33.3% of prepaid subsidization. Among caregivers in the pay-it-forward arm, 97.6% (41/42) believed that this strategy was feasible.ConclusionsThe pilot showed feasibility and preliminary effectiveness of a pay-it-forward strategy to increase HPV vaccination rate. The high uptake rate in the standard-of-care arm is likely caused by the selection bias associated with the online dissemination approach and secured vaccine supply through the program. Further adaption of the intervention package and a population-based recruitment pathway are needed to better reflect local contexts and enhance the generalizability of the subsequent formal trial.Trial registrationChinese Clinical Trial Registry (ChiCTR), ChiCTR2200055542. Retrospectively registered on 11 January 2022,https://www.chictr.org.cn/showproj.html?proj=139738.