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.
Keywords: Community immunity; Health literacy; Herd immunity; Immunization; Tragedy of the commons; Vaccine hesitancy.
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