Abstract
The prevention of cervical cancer using either the bivalent or the quadrivalent HPV vaccine is the goal of immunization programs in many countries. The vaccines, which were designed to prevent cervical cancer outcomes in adults, need to be administered before the onset of sexual activity.
Since the HPV vaccines are among the most expensive of all the widely recommended vaccines, limited financial resources restrain the HPV vaccination in some countries around world. The bivalent vaccine Cervarix, developed against the HPV types 16 and 18, contains 20 μg of antigen L1 of both these types and is formulated with the AS04 adjuvant system, which consists of 50 μg of monophosphoryl lipid A adsorbed into 500 μg of aluminum hydroxide.
Higher immunogenicity of this vaccine in young adolescents, as well as potential cost savings, have prompted discussions about the efficacy of the 2-dose HPV vaccine schedule. The immunobridging studies HPV 048 and HPV 070 showed that two doses of the bivalent HPV vaccine in girls aged 9-14 years induced geometric mean antibody titers that were non-inferior to geometric mean antibody titers elicited in women 15-25 years old with three doses of the vaccine.
Non-inferiority for HPV-16, -18, -31 a -45 was obtained for the 2-dose, month 0-6 schedule in girls 9-14 years old vs. the 3-dose, month 0-1-6 schedule in women 15-25 years old in the period of 48 months. These results indicate that the bivalent HPV vaccine applied in 2 doses has sufficient immunogenity in girls 9-14 years old.