Canadian researchers led by Salaheddin M. Mahmud, MD, PhD of the University of Manitoba conducted a study to assess the effectiveness of the quadrivalent human papillomavirus (QHPV) vaccine against cervical dysplasia.
Females 15 years old and older who received the QHPV vaccine in Manitoba between September 2006 and April 2010 (n = 3,541) were matched on age to up to three non-vaccinated females (n = 9,594). The researchers 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).
During a median follow-up of 3.1 years, vaccinated girls and women had LSIL and HSIL rates of 3.3% and 2.3%, respectively, compared with 3.7% and 2.6% for those not vaccinated. No one (vaccinated or not) developed cervical cancer during the follow-up period, but 12 vaccinated patients (0.3%) and 22 unvaccinated patients (0.2%) developed carcinoma in situ. Among girls ages 15 to 17 at enrollment, vaccine effectiveness estimates were 35% against HSIL, 21% for LSIL, and -1% for ASCUS. Women 18 years old and older without cervical abnormalities at the time of vaccination had a 23% reduction in the risk of high-grade squamous intraepithelial lesions (HSIL) when compared with unvaccinated women. However, the quadrivalent vaccine did not appear to protect against HSIL among women who had abnormal cytology at the time they were vaccinated. The researchers concluded that a significant percentage of vaccinated women may not be protected against HSIL or lesser dysplasia especially if they were vaccinated at older age or had abnormal cytology before QHPV vaccination.
Mahmud SH, Kliewer EV, Lambert P, et al. Effectiveness of the quadrivalent human papillomavirus vaccine against cervical dysplasia in Manitoba, Canada. J Clin Oncol 2013; DOI: 10.1200/JCO.2013.52.464. Published online before print 1/6/14.