How Does Communicating Herd Immunity Affect Immunization Intentions?

Abstract

While previous studies have shown that communicating herd immunity can increase immunization intentions, it is unclear how the definition of the beneficiaries influences intentions. In a vignette study, using a new hypothetical influenza virus, 4,172 participants from five European countries (Bulgaria, N=873; Denmark, N=896; England, N=873; Estonia, N=916; and Italy, N=745) were randomized to one of three experimental conditions: (1) control (no mention of herd immunity), (2) society (social benefit of immunization for overall society mentioned), and (3) friends (social benefit for friends and family members mentioned). While the study did not find that communicating herd immunity influenced overall immunization intentions across the five countries, it found substantial cross-country differences in the effect of the communication. In England, friends increased intentions, while society increased intentions in Denmark but decreased it in Italy. While communicating the social benefit of immunization can influence intentions, its contrasting effects highlight the importance of empirically testing.