About HPV Vaccines
9-valent HPV vaccine (Gardasil-9 pdf icon[23 pages]external icon) is a non-infectious recombinant vaccine prepared from the purified virus-like particles (VLPs) of the major capsid (L1) protein of HPV types 6, 11, 16, 18, 31, 33, 45, 52, and 58.
Immunogenicity and Vaccine Efficacy
- High efficacy among persons without evidence of prior infection with HPV vaccine types
- No evidence of efficacy against disease caused by HPV types with which participants were already infected at the time of vaccination
- Prior infection with one HPV vaccine type did not diminish efficacy of vaccine against the other HPV vaccine types
HPV vaccines are highly immunogenic. More than 98% of recipients develop an antibody response to HPV types included in the respective vaccines 1 month after completing a full vaccination series.
- However, there is no known serologic correlate of immunity and no known minimum titer determined to be protective.
- The high efficacy found in the clinical trials to date has precluded identification of a minimum protective antibody titer.
- Further follow-up of vaccinated cohorts may allow determination of serologic correlates of immunity in the future.
All HPV vaccines have been found to have high efficacy (close to 100%) for prevention of HPV vaccine type-related persistent infection, cervical intraepithelial neoplasia (CIN) 2/3, and adenocarcinoma in situ (AIS) in clinical trials. These trials were conducted in women aged 15 or 16 through age 26 years, following a three-dose vaccination schedule. Quadrivalent vaccine was also found to have high efficacy (99%) for prevention of genital warts. Among men who have sex with men (MSM), quadrivalent vaccine had high efficacy against anal intraepithelial neoplasia grade 2 or 3 (AIN 2/3).
Immunogenicity trials showed that the antibody response to a three-dose schedule in 9- through 14- or 15-year-olds was non-inferior to the antibody response in women in the age group in which efficacy was demonstrated in the large clinical trials. Licensure in the younger age group was based on these immunobridging data.
Immunogenicity trials conducted several years after the original vaccine licensures demonstrated that the antibody response after two doses given 6 to 12 months apart in 9- through 14-year-olds was non-inferior to the antibody response after three doses in women in the age group in which efficacy was demonstrated in the clinical trials. These studies led to approval and recommendation of a two-dose schedule in young adolescents.
For more efficacy studies, see the Pink Book Chapter on HPV.