Emphasising herd immunity in vaccine advocacy: a systematic review and meta-analysis.

Emphasising herd immunity in vaccine communication may affect vaccine uptake by eliciting prosocial or selfish motivations. While experimental evidence has accumulated, quantitative syntheses are lacking. We conducted a systematic review and three-level meta-analysis to estimate how emphasising herd immunity affects vaccination motivation. Literature up to April 2025 was searched across seven databases (CINAHL, Cochrane Library, Google Scholar, PsycINFO, PubMed, Scopus, Web of Science) without restrictions. Non-experimental studies or those not assessing vaccination motivation were excluded. Risk of bias was assessed using JBI checklists. From 5,862 records, 3,676 underwent title/abstract screening; 278 were assessed, yielding 43 included studies (67 effects), totalling 101,720 participants (51,725 vs. 49,995 for intervention vs. control groups). The pooled effect size (Hedges g = 0.12, 95% CI [0.08, 0.17], p < .001) indicated small, positive effects, but between-study heterogeneity was large (I² = 91.9%). Subgroup analysis showed a twice as large effect for experiential methods (e.g., virtual reality, simulations: g = 0.29, 95% CI [0.16, 0.42], p < .001). Study quality was adequate, without evidence of publication bias. These findings suggest that emphasising herd immunity increases vaccination motivation, especially when using experiential communication methods. Directions for future research and implications for public health campaigns are discussed.