Operationalizing outcome measures of human papillomavirus vaccination among adolescents

Objectives: When examining vaccination coverage, researchers must make decisions about how to define outcome measures based on many factors, including the timing of doses. Different operationalizations of the same outcome can often lead to different findings and can affect the ability to make comparisons across studies. This methodological article aimed to illustrate the implications of two options for operationalizing human papillomavirus (HPV) vaccination based on timing: initiation of the first dose at any age vs before the 13th birthday (on time). Study design: Cross-sectional observational design. Methods: The 2014 National Immunization Survey for Teens (N = 16,439 adolescents aged 13–17 years) was analyzed using multivariate logistic regression for each outcome measure and effect modification by gender. Results: Age was positively associated with initiation at any age but negatively associated with on-time initiation. Gender modified the effect of race/ethnicity for both measures of initiation, but the pattern across groups was different for the two outcomes. Gender modified the effect of provider recommendation for initiation at any age, while gender modified the effects of age and region for on-time initiation. Conclusion: Decisions of how to operationalize outcomes of HPV vaccine initiation among adolescents can lead to different conclusions about the role of age and gender differences for several predictive variables. To inform the development of public health efforts that promote on-time HPV vaccination among male and female adolescents, researchers should consider the importance of dose timing when operationalizing outcome measures. We recommend including on-time receipt of the HPV vaccine as an outcome measure.