Use of quadrivalent human papillomavirus vaccine and the prevalence of antibodies to vaccine-targeted strains among female service members before and after vaccination.

The quadrivalent human papillomavirus vaccine (HPV4) has been shown to generate a robust immune response among fully vaccinated individuals; however, among U.S. service members, HPV vaccine completion rates are low. This study compared the immunogenicity of HPV4 vaccine among partially and fully vaccinated service members at 4-6 years post-vaccination. A random sample was obtained of 2,091 female service members, aged 17-26 years, who received 1-3 HPV4 doses during 2006-2012, stratified by number of doses (one, two, or three). Pre- and post-immunization sera from these service members were tested for antibodies to the HPV strains covered by the vaccine. Prior to immunization 42% were seropositive for HPV strain 6; 34% for strain 11; 29% for strain 16; and 16% for strain 18. Among those naive to all four strains prior to immunization, there was 100% seroconversion after one, two, or three doses. The results indicate that many service members had already been exposed to strains of HPV prior to receiving the vaccine; however, seropositivity prevalence was lower for the oncogenic HPV strains 16 and 18. The data demonstrate sustained immunogenicity after a single dose of vaccine, with modest improvement with successive doses for all strains except 18.