Harper DM, Franco EL, Wheeler CM, et al, and HPV Vaccine Study group. Sustained efficacy up to 4-5 years of a bivalent L1 virus-like particle vaccine against human papillomavirus types 16 and 18: follow-up from a randomized control trial. Lancet. 2006;367:1247-1255. The goal of the study was to determine the long-term efficacy, immunogenicity, and safety of the bivalent human papillomavirus (HPV)-16/18 vaccine (GlaxoSmithKline) against incident and persistent infection with HPV 16 and 18 and their associated cytopathic complications.
Methods: The initial trial was done in the early 2000's and published in 2002 showing that this vaccine was almost completely protective against the 2 major HPV types associated with cervical cancer. The present study enrolled women who participated in that trial to determine long-term immunogenicity, incident infections with HPV, yearly cervical cytology, and safety.
Results: There were 776 women in the follow-up study who were followed for a mean of 48 months.
Immunogenicity: Geometric mean titers were maintained at above 500 log10 EU/mL throughout the observation period averaging 4 years. These levels are at least 133-fold higher than the mean titers for the placebo group and they are higher than natural infection with HPV-16 and HPV-18 by 17- and 14-fold, respectively. The serologic response exceeded 99% for all participants tested during the 8 periods of evaluation.
Incident infection: The frequency of persistent HPV-16/18 infection detected in cervical samples in the initial and follow-up study showed 1 in the vaccine recipient group and 16 in the control group.
Histologic abnormalities: Abnormal cytologic and histologic outcomes (cervical intraepithelial neoplasia [CIN] 1 and 2) were not detected in any vaccine recipients compared with 35 in the placebo group.
Summary: These data are summarized in the Table.
Conclusion: The authors conclude that this vaccine is highly immunogenic, safe, and effective for up to 4.5 years.
Comment: Cervical cancer is the second most common cause of cancer among women in the world. This vaccine is a remarkable achievement, but it faces some stiff challenges which include parent activist groups in the United States and access in the developing world where it is needed most. Of interest in the above study is the apparent protective effect of this vaccine against infection with HPV45 and 31 as well as HPV types in the vaccine.