Immunogenicity of bivalent HPV vaccine among partially vaccinated young adolescent girls in Uganda

Background: Investigations of vaccine efficacy and immunogenicity for adult females receiving fewer than three doses of human papillomavirus (HPV) vaccine have suggested protection against infection and precancerous lesions. We investigated the immunogenicity of bivalent HPV vaccines among adolescent girls from Uganda who received one, two, or three vaccine doses. Methods: Young girls vaccinated through a government program in Uganda were invited to participate. HPV16- and HPV18-specific antibodies were measured at ≥24 months after the last vaccine dose using an enzyme linked immunoassay in girls who received one (n= 36), two (n= 145), or three (n= 195) doses. Results: Nearly all subjects (99%) were HPV16 and HPV18 seropositive at the time of blood-draw. Geometric mean antibody levels (GMTs) were: HPV161-dose=230EU/mL, HPV162-dose=808EU/mL, and HPV163-dose=1607EU/mL; HPV181-dose=87EU/mL, HPV182-dose=270EU/mL, and HPV183-dose=296EU/mL. The GMT ratio for 2:3 doses was 0.50 (HPV16) and 0.68 (HPV18) and did not meet the non-inferiority criteria (i.e., lower bound of 97.5% confidence interval of the GMT ratio greater than 0.50). The GMT ratio for 1:3 doses for HPV16 and HPV18 was inferior, but absolute GMTs for one dose were higher than adult women who received one dose (HPV16=124EU/mL, HPV18=69EU/mL) where efficacy has been demonstrated. Conclusions: Even though immunogenicity with less than three doses did not meet a priori non-inferiority thresholds, antibody levels measured ≥24 months after last dose were similar to those of adult women who have been followed for more than eight years for efficacy.