ATLANTA — Merck & Co.'s human papillomavirus vaccine Gardasil was efficacious against persistent infections and genital warts caused by the vaccine strains in a randomized, double-blind, placebo-controlled study of more than 4,000 adolescent and young adult males.
The study, funded by Merck, was planned as a 36-month follow-up but was stopped early based on efficacy and safety data at a mean of 29 months, according to Dr. Richard M. Haupt, executive director of clinical research, Merck Research Laboratories, Whitehouse Station, N.J.
The company submitted a biologics licensing application to the Food and Drug Administration in December 2008 for the use of Gardasil in males aged 9-26 years.
“Gardasil is highly efficacious against HPV-6/11/16/18-related persistent infections and genital warts in men. This efficacy may also translate to reduced transmission of vaccine type strains between sexual partners,” Dr. Haupt said at a meeting of the Centers for Disease Control and Prevention's Advisory Committee on Immunization Practices.
The study involved 3,463 heterosexual men aged 16-23 years and 602 men aged 16-26 years who have sex with men. At baseline, just 17% of the total group was positive to at least one of the vaccine HPV strains (6, 11, 16, and/or 18) by either serology or polymerase chain reaction testing.
“This gives an idea of the great opportunity to prevent infections of all four types,” Dr. Haupt said.
The primary end point was vaccine efficacy against all external genital lesions, including condyloma and penile/perineal/perianal intraepithelial neoplasia (PIN) of any grade.
In the per-protocol population, overall efficacy was 90%, driven primarily by the prevention of genital warts: 28 of 1,408 placebo subjects developed condyloma, compared with 3 of 1,397 who received Gardasil, for an efficacy of 89%. Efficacy against PIN 1/2/3 was 100%, but the numbers were small (3 vs. 0 cases).
Efficacy against persistent infection—defined as two or more consecutive positive samples with the same HPV strain 6 months apart—was 86% (101 placebo subjects vs. 15 who got Gardasil). The vaccine was highly immunogenic, with seroconversion rates at 7 months ranging from 97% for anti-HPV-18 antibodies to 99% for anti-HPV-6. At 24 months, seroconversion rates remained high for all strains except anti-HPV-18, which dropped to 62%. Efficacy remained high against all strains, he noted.