Human Papillomavirus Vaccine: For Boys, Too?
Abstract & Commentary
By Hal Jenson, MD, FAAP
Professor of Pediatrics, Tufts University School of Medicine, Chief Academic Officer, Baystate Medical Center, Springfield, MA
Dr. Jenson is on the speaker's bureau for Merck.
This article originally appeared in the January 2007 issue of Infectious Disease Alert. It was edited by Stan Deresinski, MD. Dr. Deresinski serves on the speaker's bureau for Merck, Pharmacia, GlaxoSmithKline, Pfizer, Bayer, and Wyeth, and does research for Merck. It was peer reviewed by Connie Price, MD. Dr. Price is Assistant Professor at the University of Colorado School of Medicine. She reports no financial relationships relevant to this field of study.
Source: Block SL, et al: Comparison of the immunogenicity and reactogenicity of a prophylactic quadrivalent human papillomavirus (types 6, 11, 16, 18) L1 virus-like particle vaccine in male and female adolescents and young adult women. Pediatrics. 2006;118:2135-2145.
Synopsis: An immunogenicity study of the new quadrivalent human papillomavirus vaccine was conducted in girls and boys 10-15 years of age and young adult women 16-23 years of age. All 4 vaccine types showed 1.7-2.7-fold higher immunogenic responses among young vaccinees, supporting the implementation of a gender-neutral vaccination program.
The new Quadrivalent Human Papillomavirus (HPV) L1 virus-like particle vaccine (types 6, 11, 16, 18) was studied for immunogenicity and reactogenicity in 506 girls and 510 boys (10-15 years of age) and 513 young women (16-23 years of age). Vaccine was administered in the standard schedule of 0, 2, and 6 months. Type-specific serologies were performed in a blinded fashion using a competitive Luminex xMAP-based immunoassay (cLIA) on serum samples obtained at 0, 3, and 7 months. The seroconversion rates were > 99% by 7 months for all 4 vaccine types in each group. The geometric mean titers for all 4 types were 1.7-2.7-fold higher for young girls and boys compared to young women. The vaccine was well tolerated. Most (> 97%) injection-site adverse events were mild or moderate in intensity, with injection-site pain most frequently reported after the first dose. Fever (> 37.8°C) within 5 days of vaccination occurred significantly more frequently among boys (13.8%) and girls (12.8%) than women (7.3%). Most (96.4%) fevers were < 39°C.
Commentary
Of the more than 100 total HPV types, and the 15-20 types that are oncogenic, types 16 and 18 account for about 70% of cervical and other HPV-related genital cancers. HPV types 6 and 11 are nononcogenic and account for about 90% of all cases of classic condyloma acuminata (genital warts) and about 90% of juvenile onset recurrent respiratory papillomatosis. The quadrivalent HVP vaccine is currently recommended for all young girls at 11-12 years of age, and can be given to girls as young as 9 years of age at the discretion of the healthcare provider. It is also recommended for girls and young women 13-26 years of age who have not yet received or completed the vaccine series.
The current vaccine recommendations were developed to target prevention of cervical cancer. The study end-point for vaccine efficacy studies in women 16-23 years of age was biopsy-confirmed cervical intraepithelial neoplasia (CIN) 2/3 or adenocarcinoma in situ (AIS), which are the only surrogate clinical conditions of cervical cancer. CIN 3 is a high-grade cervical dysplasia that includes carcinoma in situ. These lesions are the immediate and obligate precursor to invasive cervical cancer and are always treated.
A bridging study was necessary to span the clinical efficacy observed in adults to efficacy in young adolescents because it was not feasible to study the efficacy of HPV vaccination to prevent cancerous lesions in young adolescents, given the long duration to develop CIN as a study outcome. Somewhat surprisingly, immune responses to HPV vaccine are higher, and inversely directly related to age, among younger vaccinees. Based on the high immunogenicity in young girls, and by reference to the immunogenicity that correlated with protection of CIN in young women, the HPV vaccine is now recommended for all young girls. Vaccination at 11-12 years of age, and even as early as 9 years of age, is important to prevent HPV infection because sexual intercourse is reported among 38% of 15-year-olds and 7.4% of 13-year-olds in the United States.
This study confirms the higher immunogenicity among younger vaccinees, including boys. Although prevention of cervical cancer is the primary outcome of universal HPV vaccination, there are important reasons to consider vaccinating young boys as well. Most importantly, men are vectors of HPV to women. Mathematical modeling of HPV vaccination schemes show that a female-only vaccination policy will likely be 35-40% less effective in preventing cervical cancer than vaccination of both genders. Second, the vaccine does provide protection against types 6 and 11, which cause about 90% of all cases of genital warts in both sexes. Vaccination would provide protection against these lesions in men.
This is the first study of the immunogenicity of the HPV vaccine in young boys, and confirms a robust immune response that warrants implementation of a gender-neutral, universal HPV vaccine schedule for all young boys as well as girls.
This article originally appeared in the January 2007 issue of Infectious Disease Alert. It was edited by Stan Deresinski, MD. Dr. Deresinski serves on the speaker's bureau for Merck, Pharmacia, GlaxoSmithKline, Pfizer, Bayer, and Wyeth, and does research for Merck.You have reached your article limit for the month. Subscribe now to access this article plus other member-only content.
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