Because Gardasil is designed to prevent HPV 6, 11, 16 and 18 disease, rather than treat an ongoing infection, the primary analysis of the study was conducted among women who were free of infection with at least one of the relevant HPV types at the start of the trial (baseline), remained free of infection with the relevant type(s) throughout the course of the vaccination period, and who received all three doses of vaccine and placebo.
In the primary study analysis, there were 41 cases of persistent infection, CIN or external genital lesions (genital warts and vaginal and vulvar lesions) caused by HPV 6, 11, 16 or 18 in the placebo group compared to four cases in women who received Gardasil (91% reduction in incidence, 95% CI: 74 to 98%) over a mean of 1.65 years of follow up. Also as a primary analysis, Gardasil prevented 83% (95% CI: 51 to 96%) of persistent infection, low-grade cervical abnormalities and precancers, and external genital lesions caused by HPV types 16 and 18 alone (23 cases in the placebo group and four cases in the vaccine group). In a secondary endpoint, Gardasil prevented 100% of persistent infections, low-grade cervical abnormalities and precancers, and external genital lesions caused by HPV types 6 and 11.
In addition, Gardasil reduced HPV 16 and 18-related abnormal Pap test results (measured as a finding of atypical squamous cells of undetermined significant, or ASC-US, with positive HPV probe, or worse diagnoses) by 94% (95% CI: 63 to 100%).
Eliav Barr, head of the HPV vaccine program at Merck Research Laboratories, said: “Women remain at significant risk for acquiring HPV infections and developing HPV-related diseases throughout their lifetime. These data build on the clinical program for Gardasil and will help us to understand the potential benefit that Gardasil may have in women through age 45.”