Recent data from a trial of a two-dose regimen of vaccination of girls aged 9-13 years in Vancouver, Canada have suggested that the immune response of girls who received only two doses was non-inferior both to that of girls who received 3 doses and to that of adult women aged 16-25 years who also received 3 doses. In a complementary study in Guanacaste, Costa Rica, vaccine efficacy (defined as 12-month vaccine type-specific infection persistence) among adult women who received either one or two doses of HPV vaccine as a part of the Phase IIb clinical trials of Cervarix (GSK) was similar to women who received all three vaccines doses.