This randomised clinical trial aims to determine whether an immunization schedule comprising two doses of Gardasil administered six months apart is non-inferior to a schedule comprising three doses administered at 0, 6 and 60 months for the prevention of HPV-16 and HPV-18 infections that persist for at least six months, up to ten years after the initial vaccination. The study hypothesis is that the two-dose schedule would offer similar protection as that of a three-dose schedule against persistent HPV-16/18 infections.