ATLANTA — The efficacy of Gardasil is becoming more apparent over time, Dr. Eliav Barr said at a meeting of the Advisory Committee on Immunization Practices of the Centers for Disease Control and Prevention.
Merck is continuing to follow subjects post marketing, with nearly 3 years of data now available from three of the premarketing trials involving more than 18,000 young women. Among those are 2.4 years for the group that was naive to all four vaccine strains of human papillomavirus (6, 11, 16, and 18) at baseline, 2.9 years for another group that was naive to 14 HPV types, and 2.8 years for a combined group of uninfected and infected women at baseline, said Dr. Barr, program head of HPV Vaccines for Merck Research Laboratories, Blue Bell, Pa.
In the per-protocol investigation comprising only those naive to the vaccine HPV strains, efficacy of the vaccine against HPV 16/18-related cervical intraepithelial neoplasia (CIN) 2/3 or adenocarcinoma in situ (AIS) is 99%, down from 100% at the time of licensure. The drop was the result of just one case of HPV 16/18-related CIN3 in a Gardasil recipient (versus 73 cases in the placebo group). An investigation into that one case determined that it was likely caused by contamination, Dr. Barr said.
Efficacy against HPV 16/18-related vulvar and vaginal intraepithelial neoplasia 2/3 remains at 100%, as it was at licensure. Efficacy against any grade of HPV 16/18-related CIN or AIS is now at 96%, compared with 95% at licensure. Efficacy continues to increase over time as more cases of HPV 16/18-related disease occur in placebo recipients. Against all vulvar and vaginal lesions, including warts, the vaccine has stayed 99% effective. It's possible that the few vaccine recipients who did develop lesions—6 CIN/AIS and 2 vulvar/vaginal lesions, compared with 148 and 189, respectively, among placebo recipients—were already infected at baseline, he noted.
In the combined group of those infected and uninfected at baseline, vaccine efficacy is now 41% against CIN 2/3 or AIS (versus 34% at licensure), 71% against vaginal or vulvar intraepithelial neoplasia 2/3 (69% at licensure), 54% against CIN of any grade (46% at licensure), and 78% against vulvar/vaginal lesions including warts, up from 70%.
Preliminary data also suggest cross-protection of the vaccine against lesions caused by nonvaccine strains of HPV.