A vaccine against human papillomavirus (HPV) protects women against two strains of the virus that causes anal cancer, researchers reported.
The vaccine (Cervarix) against HPV strains 16 and 18 offered “strong protection” against anal infection in a study whose main goal was to assess the efficacy of vaccination against cervical infection and pre-cancerous lesions, according to Aimée Kreimer, PhD, of the National Cancer Institute, and colleagues.
The protection was higher in women who did not have HPV infection when they were first given the vaccine, Kreimer and colleagues reported online in The Lancet Oncology.
Anal cancer is rare in women, with an annual incidence of about 1.5 per 100,000, but rates are rising, the researchers noted. The rate is higher than for men in general, but markedly lower than for men who have sex with men or those with HIV.
Most anal cancers are caused by HPV, with strains 16 and 18 responsible for up to 80% of cases, Kreimer and colleagues noted.
They tested the vaccine against anal infection in a subgroup of young adult women, ages 18 through 25, who enrolled in a community-based randomized trial of cervical vaccine efficacy in Costa Rica.
The 6,352 participants who came for the final blinded study visit, four years after their first of three vaccine shots, were asked to give an anal sample, and 4,210 did so, with a median follow-up of 48.1 months.
The researchers analyzed anal infection in the whole cohort and also in a subgroup of women who had been negative for HPV DNA and antibodies at the start of the trial. Patient characteristics in both groups were well-balanced, the researchers reported, including the proportions who got the vaccine and those who were in the control group, given hepatitis A vaccine.
Kreimer and colleagues found…