USING CONJOINT ANALYSIS TO IDENTIFY FACTORS THAT INFLUENCE VACCINE ACCEPTANCE

Purpose:   Identifying the most influential factors in the decision to vaccinate may help policy makers design more effective programs to increase vaccination rates.  The purpose of this study was to identify the relative importance of attributes that influence vaccine decision-making among adults, adolescents, and parents of adolescents in the United States using conjoint analysis.

Method: Twelve attributes related to vaccine uptake were selected for inclusion in a conjoint analysis based on findings from four focus groups and a literature review (Table 1).  Each attribute was assigned 2-8 possible values, or levels.   Survey respondents were given a profile of a hypothetical vaccine based on selected attribute levels and asked whether they would accept (yes/no) the vaccine for themselves (adults and adolescents) or their child (parents). Respondents could be randomly assigned to 13 different versions of the survey.  Each version contained 5 vaccine profiles, generated using a fractional factorial design, with 8 alternating attributes in each. The survey was fielded to a sample of adolescents (ages 13-17; n=1516), parents (n=1030), and non-parent adults (n=652) in November 2015 using a national probability-based online research panel.  Logistic regression with generalized estimating equations and effect coding was used to estimate the relative value of each attribute.

Result: The survey was completed by 316 adolescents, 339 parents of adolescents, and 334 adults (31% overall response rate).  Vaccine acceptance varied, with 55% of adolescents, 62% of parents, and 50% of adults willing to accept a vaccine based on the profile presented.  Adolescents were most likely to accept vaccines with high effectiveness (OR=2.43, 95% CI: 1.63-3.62), strong primary care physician (PCP) recommendation (OR=2.03, 95% CI: 1.57-2.62), and moderate cost (OR= 1.46, 95% CI: 1.09-1.97, for $75 cost after insurance).  Parents and adults had similar values, with both also indicating that high vaccine effectiveness was the most important attribute, but adults considered low cost (OR= 1.86, 95% CI: 1.36-2.55 for $10 cost after insurance) to be more influential than a strong PCP recommendation (OR=1.52, 95% CI: 1.20-1.94). 

Conclusion: Adolescents, parents and adults display consistent preferences with regards to vaccine decisions and are most sensitive to the vaccine effectiveness, followed by PCP recommendations and cost.  Health policies that focus on patient–provider communication and vaccine affordability may be effective levers to increase vaccine uptake.