The human papillomavirus 16/18 vaccine showed efficacy, sustained immunogenicity, and continued safety for up to 6.4 years in a combination of initial and follow-up placebo-controlled studies involving more than 1,000 women aged 15–26 years.
The three-country, 27-site study of the human papillomavirus (HPV) vaccine Cervarix—which is now licensed in the United States, Europe, and elsewhere around the world—was funded by GlaxoSmithKline (GSK) Biologricals. It contains the HPV types 16 and 18 adjuvanted with ASO4, comprising aluminum salt and an immunostimulatory molecule that has been shown to produce higher antibody titers that are sustained over a longer period of time, compared with the same antigens adjuvanted with aluminum salts alone, according to the GSK Vaccine HPV-007 Study Group, led by Dr. Barbara Romanowski (Lancet 2009 Dec. 3 [doi:10.1016/S0140-6736(09)61567-1]).
Of 1,113 women included in the initial study, a total of 700 completed the follow-up study. The total vaccinated cohort included 560 women in the vaccine group and 553 in the placebo group, while the according-to-protocol (ATP) efficacy cohort included 465 in the vaccine group and 454 in the placebo group. At baseline, all had normal cervical cytology and were negative for both HPV-16 and -18.
The mean follow-up period from the start of the initial study was 5.9 years, with a maximum duration of 6.4 years. The study population was racially diverse and had a mean age of 20 years (range, 15–26 years) at entry to the initial study and 23 years at the beginning of follow-up.
At 6.4 years, vaccine efficacy against incident HPV-16 or HPV-18 infection in the ATP analysis was 95.3%, and long-term efficacy against persistent infection was 100% at both 6 and 12 months. said Dr. Romanowski of the University of Alberta, Edmonton, and her study group associates.
Almost all vaccine recipients (99%) remained seropositive for anti–HPV-16 and anti–HPV-18 total IgG antibodies.
In an accompanying editorial, Dr. Gary M. Cliffordsaid that the immunogenicity data showing no evidence of further decline from 3 to 6 years are “perhaps the most interesting” because they suggest that mean antibody concentrations should remain well above those associated with natural infection long into the future.
The target age of vaccination is a balance between “being early enough to catch girls before sexual debut, but late enough to provide an as yet unknown duration of immunity that protects during as many subsequent years of sexual activity as possible,” wrote Dr. Clifford of the International Agency for Research on Cancer, Lyon, France (Lancet 2009 Dec. 3 [doi:10.1016/S0140-6736(09)61789-X]).
Disclosures: Dr. Clifford said that he had no conflicts of interest.