Message Framing in HPV Vaccination Decision

Study design We conducted a randomized survey experiment with pre-post design between December 2024 to January 6th 2025, right before the approval of the first HPV vaccine for male in the country in January 8th across three geographically dispersed Chinese universities (eastern, western, and northern regions). This study was conducted from The Institutional Review Board of Hangzhou Normal University, School of Public Health approved this study (approval no. 20240010).

Participants The proportion of male college students intending to receive the HPV vaccine was assumed to be 45% in the calculation of sample size, based on a previous report in China [28]. We assumed an increase in vaccination willingness to 55% for the personal risks group and partner risks group and 65% for the both risks group. To detect a significant intervention effect with a 2-sided α = .05, a power of 0.80, and an 80% valid response rate, we calculated that 169 participants were required (676 participants total).

From 720 initially involved in baseline evaluation, we excluded 82 due to incompleteness (>10% missing data) or invalidity (i.e., inconsistent responses to attention-check items), and 35 additional participants reporting prior HPV vaccination or definite baseline vaccination intention, yielding a final analytical sample of 612 male college students.

Randomization and interventions Participants provided electronic informed consent with voluntary withdraw options. Randomization was implemented through a 1:1:1:1 allocation ratio to four conditions: Control group (Group 1, n=154) receiving a standard statement of HPV risks (In mainland China, HPV vaccines are currently approved only for female use. However, in other countries, they are also available for males. HPV can cause cancers throughout the body, from the head to the reproductive system. Thus, HPV vaccination can protect against many cancer types. Annually, over 120,000 Chinese are diagnosed with HPV-related cancers, with about 50,000 dying from them.); Intervention 1 (Group 2, n=152) adding male-specific health risks; Intervention 2 (Group 3, n=153) adding risk to female partners; Intervention 3 (Group 4, n=153) adding both personal risk and risk to female partners. The protocol involved sequential completion of pre-exposure questionnaires, timed 120-second message exposure, and immediate post-exposure assessment.

Measures We evaluated three primary outcomes. The first outcome is vaccination intention ("If HPV vaccine were available for males in China, would you get vaccinate?"). The answer was measured using a 5-point Likert scale (1= "not at all willing" to 5= "highly willing") and then dichotomized into "willing (4-5)" vs. "unwilling (1-3)". The second outcome is Precaution Adoption Process Model (PAPM) adapted decisional readiness. A single question was asked "Before today, what do your stance on HPV vaccination?" the answer was categories as "pre-decisional (never heard/knew but no consideration) vs. "decisional (active refusal/acceptance). The third outcome aims to test the respondents' perceived responsibility toward HPV infection prevention with a single question "HPV infection is a shared responsibility of both genders." The answer was measured using a 5-point Likert scale on agreement (1= "strongly disagree" to 5= "strongly agree"). The final answer was dichotomized into "agree (4-5)" and "disagree (1-3)".

Statistical analysis Chi-square test and Kruskal-Wallis H test were performed to compare the frequencies and percentages of participants' demographic characteristics across groups. McNemar's test and Chi-square test were used to compare the effect within and between groups respectively. Multivariate logistic regression models, adjusting for sociodemographic factors (e.g., age and education background), were adopted to evaluate the differences between the four groups. All statistical analyses were performed using SPSS version 27.0, based on different statistical significance levels of p value after Bonferroni correction.