Conscious consideration of herd immunity in influenza vaccination decisions

Background: Influenza vaccination decisions may be influenced by perceived risk reduction related to herd immunity.

Purpose: This paper examines how free-riding (i.e., foregoing vaccination because of reduced risk perceptions related to herd immunity) or protective benefits to the community affect vaccination decisions.

Methods: A survey of a nationally representative panel of U.S. adults (N=442 respondents; data collected and analyzed during 2012) asked about how respondents made vaccination decisions, including whether and how vaccination among the members of respondents' social networks influenced their own vaccination decisions.

Results: Most individuals (61%) reported that vaccination in the social network would not influence their decision. Among those perceiving being influenced by vaccination in their social network, most stated that an increase in network vaccination coverage would make them more likely to get vaccinated, rather than less. Overall, only 6% (28 of 442) gave a response consistent with the reduced-risk logic of herd immunity, which was more common among those stating that they would be less likely to get vaccinated (emphasizing free-riding) than among those more likely to get vaccinated (emphasizing social protection; 33% vs 11%, two-sided, p=0.0005). The reduced-risk logic of herd immunity, and more specifically free-riding, is consciously considered by relatively few individuals. Far more common are social influences bolstering personal vaccination, such as peer pressure and social learning (6% vs 11%, two-sided, p=0.015).

Conclusions: Interventionists may be more successful by capitalizing on existing social-influence considerations than by trying to combat the conscious lure of free-riding.