A 2-dose quadrivalent human papillomavirus (HPV) vaccine series in girls may be as immunogenic as a 3-dose series in young women, according to the results of a randomized clinical trial conducted in Canada.1 However, a loss of noninferiority to some genotypes after 2 years requires additional study before a 2-dose schedule can be recommended, the study authors advised.
The CDC currently recommends a 3-dose schedule of HPV vaccine administered over 6 months for the prevention of cervical cancer and other cancers caused by infection with HPV genotypes 16 and 18.2 The vaccine works best when administered by age 12, ideally before the commencement of any sexual activity with another person; the vaccine also produces higher antibody titers when given at a younger age. However, the cost of this vaccine seems to impede its use, especially in resource-poor countries.
To assess whether mean antibody levels to HPV genotypes 6, 11, 16 and 18 among girls receiving 2 doses was noninferior to young women receiving 3 doses, researcher randomized 261 girls aged 9 to 13 years to receive 3 doses of quadrivalent HPV (given at 0, 2, and 6 months) and 259 girls to receive 2 doses (given at 0 and 6 months). In addition, 310 young women aged 16 to 26 years received 3 doses of HPV vaccine at 0, 2, and 6 months. Antibody titers were then measured at 0, 7, 18, 24, and 36 months. Follow-up blood samples were collected from 675 participants (81%).
At 7 months, geometric mean titer (GMT) ratios were noninferior for girls receiving 2 doses to women receiving 3 doses and for girls receiving 2 doses to girls receiving 3 doses for all genotypes. The GMT ratios for girls receiving 2 doses to young women receiving 3 doses remained noninferior for all genotypes up to 36 months, the study authors reported. For girls, however, the antibody response in the 2-dose group was inferior to that in the 3-dose group for HPV-18 by 24 months and for HPV-6 by 36 months.
Because of the loss of noninferiority over time for some genotypes when just 2 doses of HPV vaccine was given, a reduced-dose schedule cannot be recommended until more information is known about how the number of doses effects the duration of protection.
- Seven months after the first dose of HPV vaccine, antibody levels were comparable between girls and young women regardless of the number of doses they received.
- Compared with girls who received 3 doses of HPV vaccine, girls who received 2 doses had lower antibody titers to HPV-18 by month 24 and HPV-6 by month 36.
- A reduced-dose schedule for HPV vaccine cannot be recommended at this time.
1. Dobson SR, McNeil S, Dionne M, et al. Immunogenicity of 2 doses of HPV vaccine in younger adolescents vs 3 doses in young women: a randomized clinical trial. JAMA. 2013;309:1793-1802.
2. Centers for Disease Control and Prevention. HPV vaccine: questions & answers. Available at: http://www.cdc.gov/vaccines/vpd-vac/hpv/vac-faqs.htm. Accessed June 7, 2013.