One or two doses of the vaccine Cervarix may be as effective as the complete three-dose series against infections with high-risk human papillomavirus (HPV) types 16 and 18, according to a study published online ahead of print June 9 in The Lancet Oncology.

Lead author Aimée R Kreimer, PhD, and colleagues analyzed data from two phase 3 clinical trials of Cervarix in which women were randomly chosen to receive three doses in the standard series or a control vaccine. According to the prescribing information, Cervarix is indicated for the prevention of cervical cancer, cervical intraepithelial neoplasia (CIN) grade 2 or worse and adenocarcinoma in situ, and CIN grade 1, all of which are caused by oncogenic HPV types 16 and 18. 

The researchers evaluated the effectiveness of the vaccine in all of the women, including those who did not complete the series, for four years. Of the vaccinated cohort, 22,327 received three doses, 1,185 received two, and 543 received one.

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Efficacy against incident HPV-16/18 infections for three doses was 77%, two doses was 76%, and one dose was 85.7%. In women who received two doses, efficacy against incident HPV-16/18 infection was 75.3% for those who received their second dose at one month and 82.6% for those who received the second dose at six months.