Importance: Human papillomavirus (HPV) vaccination rates among US females remain low, in part because of concerns that HPV vaccination may promote unsafe sexual activity by lowering perceived risks of acquiring a sexually transmitted infection (STI).
Objective: To study whether HPV vaccination of females is associated with increases in STI rates.
Design, setting, and participants: Using a large, longitudinal insurance database of females aged 12 to 18 years insured from January 1, 2005, through December 31, 2010, in the United States, we examined whether HPV vaccination was associated with an increase in incident STIs among females who were vaccinated compared with those who were not. We defined STIs as one or more medical claims for any of the following infections in a given quarter: chlamydia, gonorrhea, herpes, human immunodeficiency virus or AIDS, or syphilis. We used difference-in-difference analysis to compare changes in STI rates among HPV-vaccinated females before and after vaccination (index quarter) to changes among age-matched nonvaccinated females before and after the index quarter. We analyzed whether effects varied according to age and prior contraceptive medication use.
Main outcomes and measures: Rates of STIs.
Results: The rates of STIs in the year before vaccination were higher among HPV-vaccinated females (94 of 21 610, 4.3 per 1000) compared with age-matched nonvaccinated females (522 of 186 501, 2.8 per 1000) (adjusted odds ratio, 1.37; 95% CI, 1.09-1.71; P = .007). The rates of STIs increased for the vaccinated (147 of 21 610, 6.8 per 1000) and nonvaccinated (781 of 186 501, 4.2 per 1000) groups in the year after vaccination (adjusted odds ratio, 1.50; 95% CI, 1.25-1.79; P < .001). The difference-in-difference odds ratio was 1.05 (95% CI, 0.80-1.38; P = .74), implying that HPV vaccination was not associated with an increase in STIs relative to growth among nonvaccinated females. Similar associations held among subgroups aged 12 through 14 years and aged 15 through 18 years and among females with contraceptive use in the index quarter.
Conclusions and relevance: Human papillomavirus vaccination was not associated with increases in STIs in a large cohort of females, suggesting that vaccination is unlikely to promote unsafe sexual activity.