Cervical Cancer Prevention (PDQ®): Prevention - Health Professional Information [NCI] - Evidence of Benefit
Vaccine Efficacy of the Quadrivalent HPV Vaccine
||Point Estimate and 95% CI
|CI = confidence interval; CIN = cervical intraepithelial neoplasia; HPV = human papillomavirus; ITT = intention-to-treat.
|HPV naive population for HPV-CIN 3
||100% (90.5%-100%) for lesions associated with HPV 6, 11,16, or 18
|ITT CIN 3
||45.3% (29.8%-57.6%) for lesions associated with HPV 6, 11, 16, or 18
This study also demonstrated decreased rates of abnormal Pap tests and subsequential diagnostic procedures. No cases of invasive cervical cancer were identified during the trial.
As largely expected based upon their mechanism of action, L1/2 HPV vaccines do not appear to impact pre-existing infections. The FUTURE II trial demonstrated a markedly lower vaccine efficacy rate in the total randomized study population, which included individuals positive for HPV at baseline, versus the "per-protocol" population (44% for lesions associated with HPV 16 or 18 and 17% for lesions associated with any HPV type vs. 98%, see table above). Additionally, an intermediate analysis of a randomized controlled trial primarily evaluating the efficacy of the HPV-16/18 vaccine in preventing infection found no effect on viral clearance rates in women aged 18 to 25 years who were positive at the time of study enrollment.
The type-specific vaccines, if successful in preventing invasive cancer, will offer protection for only a subset of cases, the proportion of which will vary worldwide. Using data from a multicenter case-control study conducted in 25 countries, it was estimated that a vaccine containing the seven most common HPV types could prevent 87% of cervical cancers worldwide. A vaccine with HPV-16 and HPV-18 types, the two most common strains, would prevent 71% of cervical cancers worldwide.
Anal HPV infection
Anal cancer occurs rarely: the international age-adjusted annual incidence is about 1.5 cases per 100,000 women. However, rates have been increasing in Europe and the United States over the past few decades. As with cervical cancer, HPV-16 and HPV-18 are associated with a majority of anal cancer cases. To estimate the efficacy of the bivalent vaccine against anal HPV infections in women, investigators examined a subset of women participating in a randomized controlled trial principally designed to assess vaccine efficacy against persistent cervical HPV-16/18 infections and associated precancerous lesions. In the original trial, 6,352 women aged 18 to 25 years received three doses of the bivalent vaccine or a control hepatitis A vaccine and were followed for 4 years after the first administration. Women that attended the 4-year study visit, consented to provide anal specimens, and completed a survey regarding anal sexual behaviors (n = 4,210) were included in this secondary analysis. The efficacy of the vaccine against prevalent HPV-16/18 anal infections was 62% (95% CI, 47.1-73.1) for an ITT cohort. Limitations of this study include an inability to assess the baseline anal HPV infection rate in the population or to use HPV persistence as the endpoint of interest; given a high rate of spontaneous resolution of HPV infection, the endpoint of HPV prevalence will overestimate the efficacy of the vaccine. Additionally, there was a high attrition rate: the subgroup represented 56% of the original trial participants, of which 27% were lost due to noncompliance with anal sampling. The study provides no information about the efficacy of the vaccine against precancerous anal lesions or anal cancer.