Effectiveness of the Quadrivalent Human Papillomavirus Vaccine Against Cervical Dysplasia in Manitoba, Canada

Abstract

Purpose Effectiveness of the quadrivalent human papillomavirus (QHPV) vaccine against cervical dysplasia has not been estimated using population-based individual level data. We assessed the vaccine effectiveness (VE) of the QHPV vaccine against cervical dysplasia using data collected routinely in Manitoba. Methods Females ≥ 15 years old who received the QHPV vaccine in Manitoba between September 2006 and April 2010 privately (n = 3,541) were matched on age to up to three nonvaccinated females (n = 9,594). We used Cox regression models to estimate the hazard ratios for three outcomes: atypical squamous cells of undetermined significance (ASCUS), low-grade squamous intraepithelial lesions (LSILs), and high-grade SILs (HSILs). Results Among the 15- to 17-year-olds, the adjusted VE estimates were 35% (95% CI, −19% to 65%), 21% (−10% to 43%), and −1% (−44% to 29%) against the detection of HSILs, LSILs, and ASCUS, respectively. The corresponding estimates were higher (46% [0% to 71%], 35% [10% to 54%], and 23% [−8% to 45%]) among those who had ≥ one Pap smear after enrollment. The QHPV vaccine was associated with 23% (−17% to 48%) reduction in HSIL risk among those ≥ 18 with no history of abnormal cytology, but there was no evidence of protection among those with such a history (−8% [−59% to 27%]). Conclusion A significant percentage of vaccinated women may not be protected against HSIL and lesser dysplasia especially if they were vaccinated at older age (≥ 18) or had abnormal cytology before vaccination. These findings affirm the importance of vaccination before any significant exposure to HPV occurs and underscore the need for screening programs that cover all sexually active women, even if they were vaccinated.