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A post hoc analysis was performed using combined data from two Phase I tolerability/immunogenicity studies of monovalent human papillomavirus type 11 (HPV11) or HPV16 L1 virus-like particle (VLP) vaccines. The goal was to determine if the HPV16 L1 VLP vaccine protected against HPV16 infection. Vaccine or placebo was given at 0, 2 and 6 months. HPV16 infection was defined by positive polymerase chain reaction (PCR) results following vaccination. The incidence of HPV infection was observed to be 0 cases per 100 person-years at risk in the vaccine group, and 5 cases per 100 person-years at risk in the control group. These results support the institution of larger efficacy trials for HPV L1 VLP vaccines.

Two candidate vaccines to prevent infection with human papillomavirus (HPV) Types 11 and 16 were studied in similar double-blind, placebo-controlled, dose-escalation trials. L1 virus-like particle (VLP) vaccines were made from recombinant L1 capsid protein of HPV11 or HPV16. Participants received 10, 20, 50, or 100 microg of HPV11 L1 VLPs, 10, 40, or 80 microg of HPV16 L1 VLPs, or placebo at Months 0, 2, and 6. Serum geometric mean antibody levels at Month 7 were 258, 644, 647, and 1112 milli-Merck units (mMU)/ml for the 10, 20, 50, and 100 microg doses of the HPV11 L1 VLP vaccine, respectively, and 479, 808, and 732 mMU/ml for the 10, 40, and 80 microg doses of the HPV16 L1 VLP vaccine, respectively. Antibody to HPV11 and 16 was still present at Month 36 in 96.8 and 93.5% of vaccinees, respectively. Both vaccines were well tolerated and were associated with only mild to moderate injection-site reactions.