Psychological inoculation protects young women in South Africa against HIV prevention misinformation: Evidence from a randomised controlled trial

Background Misinformation decreases public confidence in health technologies and willingness to use them. Psychological inoculation, or "prebunking", exposes people to misleading claims before they spread widely and refutes the claims and embedded persuasion tactics. Evidence on its effectiveness for HIV-related misinformation, particularly in sub-Saharan Africa and among young women (a population highly vulnerable to HIV), is limited. Methods We conducted a randomised controlled trial (July to October 2025) among 2,163 women aged 18-29 years recruited online in South Africa. Participants were randomly assigned to view two short TikTok-style inoculation videos addressing common myths about an HIV vaccine, or attention-matched control videos on nutrition and diabetes. All participants then viewed multiple false claims presented as social media posts. The primary outcome was intention to receive an HIV vaccine if available (1-10 scale), assessed immediately post-intervention and at three-week follow-up. Secondary outcomes included likelihood of recommending the vaccine; and perceived credibility, emotional impact, and shareability of misinformation claims. We used linear regression models to estimate intervention effects. Results Misinformation exposure reduced vaccine intentions by 0.63 points in the control group, while intentions increased by 0.30 points in the intervention group. Controlling for covariates and baseline intentions, post-exposure vaccine intentions were 0.92 points higher in the intervention group (95% CI 0.78, 1.06; p<0.01), a 12% relative increase. Intervention participants were also more likely to recommend the vaccine (+0.74; 95% CI 0.61, 0.88; p<0.01). Inoculation reduced perceived credibility, emotional distress, and sharing intentions across all false claims. Effects persisted at three-week follow-up (vaccine intentions: +0.97; 95% CI 0.78, 1.17; p<0.01). Conclusion Brief, scalable psychological inoculation delivered via social-media-style videos protected young women's HIV vaccine intentions, with effects generalising to novel claims and persisting over three weeks. Prebunking campaigns may safeguard public confidence in other new HIV prevention technologies like lenacapavir.