Using the precaution adoption process model to clarify human papillomavirus vaccine hesitancy in canadian parents of girls and parents of boys.

: Achieving optimal human papillomavirus (HPV) vaccine uptake can be delayed by parents' HPV vaccine hesitancy, which is as a multi-stage intention process rather than a dichotomous (vaccinated/not vaccinated) outcome. Our objective was to longitudinally explore HPV related attitudes, beliefs and knowledge and to estimate the effect of psychosocial factors on HPV vaccine acceptability in HPV vaccine hesitant parents of boys and girls. : We used an online survey to collect data from a nationally representative sample of Canadian parents of 9-16 years old boys and girls in September 2016 and July 2017. Informed by the Precaution Adoption Process Model, we categorized HPV vaccine hesitant parents into and . Measures included sociodemographics, health behaviors and validated scales for HPV and HPV vaccine related attitudes, beliefs and knowledge. Predictors of HPV vaccine acceptability were assessed with binomial logistic regression. : Parents of boys and girls categorized as "flexible" hesitant (i.e., ) changed over time their HPV related attitudes, behaviors, knowledge and intentions to vaccinate compared to "rigid" hesitant (i.e., ) who remained largely unchanged. In "flexible" hesitant, greater social influence to vaccinate (e.g., from family), increased HPV knowledge, higher family income, white ethnicity and lower perception of harms (e.g., vaccine safety), were associated with higher HPV vaccine acceptability. : HPV vaccine hesitant parents are not a homogenous group. We have identified significant predictors of HPV vaccine acceptability in "flexible" hesitant parents. Further research is needed to estimate associations between psychosocial factors and vaccine acceptability in "rigid" hesitant parents.