The Costa Rica Vaccine Trial for human papillomavirus (HPV) in young women has had a “modest” impact on gynecologic outcomes in the first few years of the program.
Data shows that the impact of vaccination on rates of cervical cytology screening, colposcopy, and treatment was greatest among women with no evidence of prior HPV exposure (“HPV-naïve”).
The 4-year trial involved 7466 women aged 18–25 years who were randomly assigned to receive either HPV or hepatitis A vaccination (control). For this post-hoc analysis, Ana Rodriguez (INCIENSA Foundation, San José, Costa Rica) and colleagues focused on the 6844 women who were sexually active and provided cervical samples, of whom 2284 were HPV-naïve.
Reporting their findings in the American Journal of Epidemiology, Rodriguez et al show that women who received the HPV vaccination were significantly less likely to have an abnormal cytologic diagnosis of high-grade squamous intraepithelial lesion during the 4-year trial than controls, at 6.5% versus 7.5%, a relative risk reduction of 12.4%.
HPV vaccination had a greater impact in HPV-naïve women ,with a relative risk reduction of 20.3% versus control.
HPV vaccination was also associated with a reduction in referrals for colposcopy versus control; again, this was true both for the overall cohort (28.7% vs 31.1%) and in HPV-naïve women (15.0% vs 19.0%), giving relative risk reductions of 7.9% and 21.3%, respectively.
Moreover, HPV-vaccinated women had fewer loop electrosurgical excision procedures than controls in both the overall cohort (5.0% vs 5.7%) and in the HPV-naïve group (1.1% vs 1.9%), giving relative risk reductions of 11.3% and 45.6%, respectively.
Rodriguez et al note that while the impact of HPV vaccination on healthcare use is greatest in HPV-naïve women, these represent only one-third of the 18–25-year-old population. Thus, the overall impact of vaccination is only modest, even in regions with high coverage.
“Any program aiming to measure the effect of vaccination on screening programs will need to incorporate long-term surveillance,” they conclude.