Immunogenicity of bivalent HPV vaccine among partially vaccinatedyoung adolescent girls in Uganda

Abstract

Background: Investigations of vaccine efficacy and immunogenicity for adult females receiving fewerthan three doses of human papillomavirus (HPV) vaccine have suggested protection against infection andprecancerous lesions. We investigated the immunogenicity of bivalent HPV vaccines among adolescentgirls 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 usingan 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= 230 EU/mL, HPV162-dose= 808 EU/mL,and HPV163-dose= 1607 EU/mL; HPV181-dose= 87 EU/mL, HPV182-dose= 270 EU/mL, andHPV183-dose= 296 EU/mL. The GMT ratio for 2:3 doses was 0.50 (HPV16) and 0.68 (HPV18) anddid not meet the non-inferiority criteria (i.e., lower bound of 97.5% confidence interval of the GMT ratiogreater than 0.50). The GMT ratio for 1:3 doses for HPV16 and HPV18 was inferior, but absolute GMTs forone dose were higher than adult women who received one dose (HPV16 = 124 EU/mL, HPV18 = 69 EU/mL)where efficacy has been demonstrated.Conclusions: Even though immunogenicity with less than three doses did not meet a priori non-inferioritythresholds, antibody levels measured ≥24 months after last dose were similar to those of adult womenwho have been followed for more than eight years for efficacy.