Evidence of Benefit
A multicenter, double-blind, placebo-controlled trial enrolled 2,391 women aged 16 to 23 years and randomly assigned them to receive either 40 µg of HPV-16 L1 VLP vaccine or placebo on day 1, at 2 months, and at 6 months. Papanicolaou (Pap) tests and genital samples for HPV-16 DNA were obtained on day 1, at 7 months, and every 6 months for 48 months. Colposcopy and cervical biopsies were obtained when clinically indicated at study exit. Serum HPV-16 antibody titers were obtained at study entry, at 7 months, and then every 6 months. A total of 1,505 women (755 receiving vaccine and 750 receiving placebo) completed all three vaccinations and had follow-up after month 7. After immunization, HPV titers peaked at month 7, declined through month 18, and then stabilized in months 30 through 48. There were no cases of cervical intraepithelial neoplasia (CIN) in the vaccine-treated women, but there were 12 cases in the placebo group (six CIN 2 and six CIN 3). HPV-16 infection that persisted for at least 4 months was seen in seven vaccine-treated women versus 111 placebo-treated women.
An international, double-blind, placebo-controlled trial of a bivalent HPV-16/HPV-18 VLP vaccine was performed in 1,113 women aged 15 to 25 years with normal cervical cytology who were seronegative for HPV-16, HPV-18, and 12 other oncogenic HPV types at enrollment. Women received either vaccine or placebo at 0, 1, and 6 months and were assessed by cervical cytology and self-obtained cervicovaginal samples for at least 18 months. A masked treatment allocation follow-up study was performed for an additional 3 years, for a combined analysis of up to 6.4 years of follow-up. The 12-month persistent infection rate of HPV-16 or HPV-18 in an "according-to-protocol" cohort (i.e., women who received all three doses of vaccine or placebo on the correct schedule) was 0 of 401 women in the vaccine arm versus 20 of 372 women in the placebo arm, with a vaccine efficacy of 100% (95% confidence interval [CI], 81.8-100). Diagnoses of CIN 2 or higher in a "total vaccinated" cohort (i.e., women who received at least one dose of vaccine or placebo) were 0 of 481 women in the vaccine arm versus 9 of 470 women in the placebo arm, with a vaccine efficacy of 100% (95% CI, 51.3-100). Adverse events were similar in vaccinated and placebo-treated women. It is important to note that neither analysis was intention-to-treat (ITT), making it difficult to know what the true vaccine efficacy for either virological or cytohistological endpoints would be in the routine clinical setting. Furthermore, cytohistological outcomes were reported only as composite endpoints (CIN 2+), making it impossible to distinguish the vaccine's efficacy against invasive cervical cancer alone and potentially inflating the observed efficacy by including lesions with a relatively high probability (approximately 50% for CIN 2 ) of spontaneous regression.