Background: Despite high pre-exposure prophylaxis (PrEP) awareness and willingness among Chinese men who have sex with men (MSM), actual uptake remains critically low. The health action process approach (HAPA) is a 2-phase theory that addresses both the motivational and volitional phases of health behavior change, making it suitable for tackling the intention-behavior gap in PrEP use. In China, where PrEP is not covered by national health insurance, financial barriers further hinder uptake. Group-based conditional economic incentives (GCEIs) represent an innovative strategy to address cost-related disincentives by leveraging peer influence. Objective: This randomized controlled trial aims to evaluate the effectiveness of HAPA-driven interventions, both alone and combined with GCEI, to enhance PrEP initiation and adherence among high-risk, PrEP-naive MSM in China. Methods: High-risk HIV-negative MSM naïve to PrEP were recruited via community-based organizations in 3 Chinese cities. Participants underwent individual randomization to 3 arms: (1) HAPA-based cognitive behavioral intervention featuring tailored WeChat messages and 2 structured motivational interviews targeting stage-specific barriers; (2) combined HAPA intervention with GCEI linked to peer group initiation rates, incorporating facilitated offline group activities; or (3) standard care control receiving nonpersonalized HIV prevention information. The physician-prescribed PrEP initiation rate at 3 months serves as the primary outcome. Secondary outcomes include PrEP adherence, HIV risk perception, PrEP-related stigma, and intervention acceptability. Analysis follows intention-to-treat principles using mixed-effects models. Results: The study protocol received ethics approval in December 2024 and was funded in December 2025. As of August 2025, 3 community-based organizations in Mianyang, Zibo, and Hohhot have agreed to participate. Preliminary testing has led to refinements in the WeChat mini-program, questionnaires, and motivational interview scripts. Data collection commenced in October 2025 and is projected to be completed by August 2026. As of February 2026, baseline recruitment is complete, with 381 eligible participants enrolled and randomized. The baseline characteristics were balanced across the 3 arms. Outcome data will be collected after the intervention. Data analysis is ongoing, with full results expected to be published before December 2026. Conclusions: This study rigorously tests a novel intervention integrating the HAPA with a GCEI model. By addressing both individual cognitive-behavioral barriers and financial disincentives within a supportive group context, this approach offers a potentially scalable strategy to bridge the PrEP uptake gap in China. Findings will provide critical evidence on combining theory-driven behavioral techniques with peer-group economic incentives for HIV prevention.

Background: Influenza poses a substantial health burden, especially among older adults in China. While vaccination is one of the most effective preventions, influenza vaccine uptake rates among Chinese older adults remain low. This study examines the individual and combined effects of behavioral interventions based on the Information–Motivation–Behavioral Skills (IMB) model and economic incentives in promoting influenza vaccine uptake among older adults living in China. Methods: The study will recruit 640 older adults living in eight communities that have not been covered by the free influenza vaccination policy. These eight communities (as clusters), stratified by urban and rural, will be randomized to four parallel arms, including a usual care arm, an IMB-based behavioral intervention arm, a conditional economic incentive arm, and a combined behavioral-economic arm. The interventions will start from the beginning of the flu season and last for about one month. Specifically, the IMB-based behavioral intervention encompasses health education brochures, healthcare provider-led lectures, interactive quizzes, and personalized consultations. The exact number of economic incentives is conditional on the timing of vaccination (a higher amount for early immunization) and the number of people within a household to be vaccinated at the same appointment (a higher amount for more people). The primary outcome is the influenza vaccination rate. Data will be gathered through vaccination records and questionnaires covering IMB-based vaccination cognitions. Mixed-effects models will be used to analyze the outcome of vaccination rate, reporting difference-in-differences estimates with 95% confidence intervals. Conclusions: The results of this study have the potential to inform influenza vaccination program scaleup among older adults who are not yet covered by the free influenza vaccination policy. Ethics and dissemination: Ethics approval has been granted by the ethics commission of Peking University Health Science Centre (IRB00001052-24090). Participants will be required to sign a written consent form. Findings will be reported in conferences and peer-reviewed publications in accordance with the recommendations of the Consolidated Standards of Reporting Trials. Registration number: This study was registered at the Chinese Clinical Trial Registry (ChiCTR2400090229).