Predicted Uptake of HPV Vaccines among Adolescent Girls: Impact of School Mandates

Background:
The impact of human papillomavirus (HPV) vaccination on cervical cancer rates has been predicted using mathematical models. However, a limitation of these studies is their assumption of near-instantaneous, widespread vaccine uptake among adolescent girls.

Objectives:
1) To develop a more realistic mathematical model of adolescent HPV vaccine uptake that incorporates existing data on parental attitudes and adolescent health care utilization patterns. 2) To use this model to evaluate the potential impact of school mandates for HPV vaccination.

Methods:
We developed a dynamic, compartmental model of adolescent HPV vaccine uptake that spanned a 50 year time period. Model parameters were derived from existing data on parental attitudes about HPV vaccines, validated models of health behavior, adolescent health care utilization patterns and census data.

Results:
Under baseline conditions, our model predicted that in the first year of HPV vaccination programs first, second and third doses of vaccine would be received by 25%, 17% and 7% of adolescent girls, respectively. 70% vaccination coverage, the lower threshold value used in previous studies assessing the impact of HPV vaccination on cervical cancer rates, was not achieved until year 23 of the program. Vaccine coverage after 50 years was 79%. Instituting school mandates increased HPV vaccine utilization substantially, resulting in 19% of adolescent girls fully vaccinated at after the first year, and 70% vaccination coverage by year 8. Maximal vaccination coverage, 90%, was achieved by year 43 of the program.

Conclusions:
Given current parental sentiments about HPV vaccination and existing patterns of adolescent health care utilization, our results suggest that assumptions about HPV vaccine uptake among adolescents may have been far too generous in previous models. Without strong school mandates, it make take several decades for HPV vaccination rates to reach the levels assumed in previous models of the vaccine's impact on cervical cancer.