- Category: Human Papillomavirus (HPV)
- Published on Tuesday, 30 August 2011 00:00
- Written by Liz Highleyman
The Cervarix human papillomavirus (HPV) vaccine reduced anal infection with cancer-causing HPV types 16 and 18 in a study of women in Costa Rica, according to a report in the September 2011 issue of The Lancet Oncology.
Human papillomavirus can trigger abnormal cell growth. Some types are responsible for warts, while others -- primarily 16 and 18 -- cause genital, anal, and mouth/throat cancers. HIV positive people are more susceptible to HPV infection and development of cervical and anal cell abnormalities than can progress to cancer.
Cervarix (made by Glaxo SmithKline) is a bivalent vaccine designed to protect against HPV 16 and 18. Another vaccine, Gardasil (made by Merck), is effective against HPV types 6, 11, 16, and 18. Both vaccines are approved and recommended for all girls and young women; Gardasil is also approved, though not recommended, for boys and young men. The vaccines work best when administered to young people before they become sexually active.
Aimée Kreimer from the U.S. National Cancer Institute and fellow investigators with the CVT Vaccine Group assessed the efficacy of the bivalent vaccine against anal infection with HPV type 16, type 18, or both in woman age 18-25 years.
The present analysis included 4210 women (out of a total study population of 6352) in a larger randomized, double-blind trial of Cervarix for prevention of cervical HPV 16/18 infection and associated precancerous lesions. Women were in good general health and were not pregnant or breastfeeding; this study did not look at women with HIV.
Participants were randomly assigned (1:1) to receive Cervarix or a hepatitis A vaccine as a control. Vaccines were administered at enrollment, at 1 month, and at 6 months. Follow-up continued for 4 years on average, and women were tested for both cervical and anal HPV infection. Participants were stratified according to whether they were seronegative for HPV 16 and 18 at study entry.
- In the full cohort, Cervarix was 62.0% effective against anal HPV 16 and 18 infection at 4 years, compared with 76.4% efficacy against cervical infection.
o Efficacy against anal HPV 16 alone was 68.2%;
o Efficacy against anal HPV 18 alone was 55.5%.
- Looking only at women who were HPV 16/18 negative at baseline, vaccine efficacy against anal HPV infection was 83.6%, statistically similar to the 87.9% efficacy against cervical infection.
- Among participants who reported engaging in anal sex (a risk factor for HPV), 73.9% of Cervarix recipients were free of HPV 16 and 18 at 4 years, compared with 55.3% of women who received the control vaccine.
- Cervarix also provided protection against HPV types 31, 33, and 45, which are less common causes of cervical and anal cancer.
Based on these findings, the study authors concluded that Cervarix "affords strong protection against anal HPV infection, particularly among women more likely to be HPV naive at enrollment."
Anal cancer is uncommon among women (about 1.5 cases per 100,000 per year), though their incidence rate is twice that of men overall. The risk is much higher among men who have sex with men (MSM) and men with HIV; the incidence among HIV positive gay men is estimated at 80 cases per 100,000 per year.
Regular cervical Pap screening to detect abnormal cells has dramatically reduced the risk of death due to cervical cancer. Many experts believe HIV positive people -- especially MSM -- should receive anal Pap smears, although this is currently not generally considered to be standard-of-care.
Cervarix (like Gardasil) would be expected to prevent anal cancer among men as well as women. However, given that it works best when administered to adolescents and young adults, its benefits may be limited for older people.
In an editorial accompanying the Lancet Oncology report, Diane Harper and Stephen Vierthaler from the University of Missouri School of Medicine said that protection against these cancer-causing HPV types in women "increases their benefits from vaccination," but the cost-effectiveness of the vaccine will depend on its durability, which has not yet been determined.
"Without duration of efficacy of at least 15 years, cancers will not be prevented for women or men who have sex with men, only postponed," they wrote.
AR Kreimer, P González, HA Katki, et al. for the CVT Vaccine Group. Efficacy of a bivalent HPV 16/18 vaccine against anal HPV 16/18 infection among young women: a nested analysis within the Costa Rica Vaccine Trial. The Lancet Oncology12(9):862-870 (abstract). September 2011.
DM Harper and SL Vierthaler. Who should be targeted for vaccination against anal cancer? The Lancet Oncology12(9):828-829. September 2011.