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Description: Emphasizing herd immunity, a key public health concept often highlighted in vaccine advocacy, could increase or decrease the motivation to get vaccinated due to prosociality or selfishness, respectively, or have no effect at all. Although much research investigated the effects of emphasizing herd immunity, a quantitative research synthesis of the available evidence is lacking. We therefore synthesized findings from more than ten years of experimental research regarding the effect of emphasizing herd immunity (vs. not) on vaccination intention and behavior. A systematic review and three-level meta-analysis was conducted, utilizing forward and backward citation searches, as well as searching the literature, until May 2024 available in Google Scholar, PubMed, PsychINFO, The Cochrane Library, Scopus, CINAHL, and Web of Science. No language or other formal criteria restrictions were applied. Studies were excluded if they were non-experimental or did neither assess vaccination intention nor actual uptake. Risk of bias was assessed using Joanna Briggs Institute checklists. The synthesis was preregistered with PROSPERO (CRD42024540536). Our search yielded 5863 records. 3935 were screened by title and abstract, and 281 full-text records assessed for eligibility. A total of 41 eligible studies remained (65 effect sizes), with 100678 participants, of which 50826 were allocated to intervention groups and 49852 to control groups. The pooled standardized mean difference (SMD) indicated a small positive effect of emphasizing herd immunity on vaccination intention or uptake, SMD=0·13 (95% CI 0·08 to 0·18, p < 0·001) compared to any control/comparator. Between-study heterogeneity was high (I2=91·2%). The communication medium was identified as a moderator, such that experiential methods (VR, simulations) were associated with larger effects. No evidence for publication bias was found. Emphasizing herd immunity has a small positive effect on the motivation to get vaccinated. The communication is more effective when using more elaborate and experiential communication