The new combined analysis of two independent trials strengthens previous findings from the NCI Costa Rica HPV Vaccine Trial (CVT) which reported that young women who received three, two, or one dose of the bivalent vaccine were equally protected against infection with HPV-16/18 for at least 4 years after vaccination.
Due to the lack of efficacy data on fewer than three doses, the researchers conducted a post-hoc analysis combining data from the CVT that included 7466 healthy women aged 18-25 years old and the Papilloma Trial against Cancer in Young Adults (PATRICIA) trial in 18644 healthy women aged 15-25 years from Asia-Pacific, Europe, Latin America, and North America.
High vaccine efficacy was seen against incident HPV-16/18 infections regardless of the number of doses received. This result was also observed in a subgroup of women with no sign of HPV infection either before or at the time of first vaccination, suggesting that these results are relevant to sexually-naive girls in the recommended age range for HPV vaccination (ie, 11-12 years).
In further analyses, partial protection against other HPV types not included in the vaccine formulation was seen among women who received two doses 6 months apart, similar to that reported for three doses.
However, the authors caution that more data are needed before policy guidelines can be changed.
The study is published in The Lancet Oncology.
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