COMPARING THE CONCERNS AND BIASES OF VACCINATING AND NON-VACCINATING PARENTS: A QUESTION OF DEGREE, NOT CHARACTER

Purpose: We explored whether parental beliefs regarding measles and the MMR vaccine are qualitatively different between parents who have not vaccinated all of their children and those who have.

Methods: Parents (N=203) were recruited via parenting email lists in six US cities to complete an online survey. Participants answered questions about their beliefs regarding the MMR vaccine and herd immunity. Primary outcome measures were perceived likelihood their child would experience various actual and perceived MMR vaccine side effects (e.g., fever, seizures, autism), perceived vaccination rate required for herd immunity against measles, and the perceived efficacy and importance of herd immunity. Participants also indicated whether they had vaccinated all of their children (above a year old).  

Results: Approximately a quarter of parents reported that they had not vaccinated all of their children against the measles, with the remainder reporting that all their children were vaccinated. Unsurprisingly, non-vaccinating parents thought their child was more likely to experience any of the side effects relative to vaccinating parents (all p's<.01; see Table 1). However, even vaccinating parents expressed non-trivial concern about the likelihood of the side effects occurring, even for “side effects” such as autism (p's<.01). Both groups under-estimated the effective herd immunity rate (p's<.001), with non-vaccinating parents having significantly lower estimates for the percentage of the population that needs to be vaccinated for herd immunity to be effective (p<.001). Compared to vaccinating parents, non-vaccinating parents also perceived herd immunity as being less effective at preventing the measles and that it was less important for people to get vaccinated to provide herd immunity for those who could not get vaccinated (p's<.01), but even vaccinating parents did not completely believe that herd immunity was extremely effective or important (p's<.001). 

Conclusions: While the beliefs of non-vaccinating parents and vaccinating parents were statistically different from each other, the differences appear to represent a difference in degree, rather than a difference in kind. Even vaccinating parents report non-trivial levels of concern and biased likelihood perceptions suggesting that the beliefs of non-vaccinating parents may be better characterized as amplifications of concerns and issues common to all parents. Acknowledging that most parents, even vaccinating parents, have concerns about the MMR vaccine may be one method to reduce defensiveness to vaccine-promoting information.