Interventions to help people understand community immunity: A systematic review.

BACKGROUND: Herd immunity, or community immunity, occurs when susceptible people in a population are indirectly protected from infection thanks to the pervasiveness of immunity within the population. In this study, we aimed to systematically review interventions designed to communicate what community immunity is and how community immunity works to members of the general public. METHODS: We searched PubMed, EMBASE, CINAHL, the Cochrane Central Register of Controlled Trials and Web of Science for peer-reviewed articles describing interventions with or without evaluations. We then conducted web searches with Google to identify interventions lacking associated publications. We extracted data about the target population of the interventions, the interventions themselves (e.g., did they describe what community immunity is, and how it works), any effects of evaluated interventions, and synthesized data narratively. RESULTS: We identified 32 interventions: 11 interventions described in peer-reviewed articles and 21 interventions without associated articles. Of the 32 interventions, 5 described what community immunity is, 6 described the mechanisms of how community immunity occurs and 21 described both. Fourteen of the 32 addressed infectious diseases in general while the other 13 addressed one or more specific diseases. Twelve of the 32 interventions used videos, 7 used interactive simulations and 6 used questionnaires. Ten of the 11 peer-reviewed articles described studies evaluating at least one effect of the interventions. Within these 10, 4/4 reported increased knowledge, 3/5 reported shifts of attitudes in favour of vaccination, 2/5 reported increased intentions to vaccinate. Of 3 studies evaluating interventions specifically about community immunity, 2 reported increased intentions to vaccinate. CONCLUSIONS: A compelling benefit of vaccination exists at the population level in the form of community immunity. Identifying ways to optimally communicate about this benefit may be important, because some evidence suggests that effective communication about community immunity can increase vaccination intentions.