The bivalent human papillomavirus (HPV) vaccine (Cervarix, GlaxoSmithKline), used in the routine vaccination of girls against cervical cancer, also protects against HPV infection that can lead to anal cancer.

Effects were particularly noted when the vaccine was given to women before exposure to the virus. The findings suggest that this vaccine might prevent a large proportion of anal cancers in women.

Although anal cancers remain rare in the general population, in recent decades rates have nearly doubled in many countries, including the USA and several European countries. Women have twice the incidence of anal cancer compared to men.

A large proportion of anal cancers are caused by HPV, with high-risk types HPV 16 and HPV 18 responsible for 75–80% of anal cancers.

The bivalent vaccine targets HPV types 16 and 18 and is used in the routine vaccination of girls against cervical cancer, and could offer additional protection against anal cancers associated with HPV infection.

Aimée Kreimer of the National Cancer Institute, National Institutes of Health, Bethesda, USA, and colleagues assessed the efficacy of the bivalent vaccine to reduce anal HPV 16 and HPV 18 infection using data from a randomised trial of women in Costa Rica.

The analysis included 4210 healthy women aged 18–25 years. Women were randomly assigned to receive the bivalent HPV vaccine or a control (Hepatitis A) vaccine, given in three doses—at enrolment, 1 month, and 6 months. Women were tested after 4 years for anal and cervical HPV 16 and 18 infections to assess the vaccine's efficacy.

The vaccine had 62% efficacy against HPV anal infection in the general population of young women, regardless of prior exposure to HPV, compared with nearly 77% efficacy against HPV cervical infection.

In women who likely did not have previous exposure to HPV infection, the vaccine prevented anal HPV infection in nearly 84%, which was similar to its efficacy against cervical HPV infection (nearly 89%).

The vaccine also showed, for the first time, cross-protective efficacy against other cancer-causing HPV types 31, 33 (this was not significant for HPV33), and 45 at an extragenital site, confirming that the protection offered by the vaccine goes beyond the HPV types included in the formulation.

The authors say: "HPV vaccines have great potential for prevention of a large proportion of HPV-associated cancers at the anus and other anatomical sites, assuming adequate duration of protection. In women, published evidence exists for vaccine efficacy against HPV 16 and HPV 18 infections at the cervix, vagina, vulva, and now anus."

They conclude: "Since our data show a reduction of anal HPV infection rates among vaccinated women, it suggests that in the future, women who receive the prophylactic HPV vaccines before exposure to the virus will likely have less anal cancer."

In a Comment, Diane Harper and Stephen Vierthaler from the University of Missouri-Kansas City School of Medicine, Kansas City, USA discuss who should be targeted for vaccination against anal cancer.

They say: "The additional protection against four oncogenic anal HPV types in women increases their benefits from vaccination. For men who have sex with men, HPV vaccination for anal cancer prevention is very cost effective, but, cost-effectiveness analyses for women and for men who have sex with men pivot on the duration of vaccine efficacy. 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."

Source:  The Lancet