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.

What is herd immunity, and how does it relate to pediatric vaccination uptake? US parent perspectives

In light of current concern over pediatric immunization rates, 53 US parents with at least one child kindergarten age or younger were surveyed and interviewed regarding vaccine decision making. Data were collected in 2014 in San Diego, California. Herd immunity was not a salient issue: only six (11.3%) referenced the term or concept spontaneously; others had to be prompted. Parents familiar with herd immunity (70%) variously saw it as not just unnecessary but unproven, illogical, unrealistic, and unreliable. For instance, parents questioned its attainability because many adults do not immunize themselves. Some understood the concept negatively, as an instance of "herd mentality." Further, having knowledge of herd immunity that public health experts would deem 'correct' did not lead to full vaccination. Implications of findings for understanding how the public makes use of scientific information, the potential role of public health messaging regarding altruism and 'free-riding,' and assumptions that vaccine-cautious parents would willfully take advantage of herd immunity are explored in relation to parent role expectations and American individualism.