 A ninevalent HPV vaccine Gardasil-9 has been recently approved for clinical use. No data on immunogenicity and safety of interchangeable use of the ninevalent and the bivalent vaccine Cervarix are available. The main objective of this study is to assess the immunogenicity of ninevalent and bivalent HPV vaccines when administered to 9-10-year-old girls and boys according to 0-6 month schedule. 