Vaccination could prevent infection with anal cancer-associated HPV strains in older gay men

A large number of infections with anal cancer-associated strains of human papillomavirus (HPV) among older gay men could be prevented with the use of HPV vaccines, Australian research presented to the recent 7th International AIDS Society Conference on HIV Pathogenesis, Treatment and Prevention in Kuala Lumpur shows.

HIV-positive men were especially likely to have anal infection with a high-risk strain of HPV at baseline and to have incident infections over three years of follow-up.

Investigators from the Study of the Prevention of Anal Cancer (SPANC) in Sydney undertook the research because of the high prevalence of anal HPV infection among gay men, especially those infected with HIV.

Persistent infection with a high-risk strain of HPV can lead to anal cell changes that can lead to cancer. The rate of anal cancer is especially high among HIV-positive gay men at 100 cases per 100,000.

The quadrivalent HPV vaccine (qHPV, Gardasil) provides a high degree of protection against infection with HPV types 6, 11, 16 and 18; types 6 and 11 are associated with genital warts and types 16 and 18 with anal and genital cancers. In Australia, the vaccine has been recommended for school-age girls since 2007 and for boys since 2013. The vaccine is approved for women up to the age of 45 and recommended only for men aged 26 and under, due to a lack of data in older male populations.

A nonavalent HPV vaccine (nHPV) is currently being developed by Merck & Co. This is designed to provide protection against a broader spectrum of HPV genotypes including HPV 6, 11, 16, 18, 31, 33, 45, 52 and 58.

Investigators wanted to establish the potential impact of vaccination with qHPV or nHPV on the incidence of anal HPV infection among older gay men. They especially wanted to see if HIV infection and age were risk factors for infection with high-risk strains of HPV.

A total of 342 gay men aged 35 and older were recruited to the study between 2010 and 2013. They were screened at baseline for infection with HPV types covered by qHPV and nHPV. Over three years of follow-up, the participants were also examined for incident high-risk HPV infections.

The participants had a mean age of 49 years (range: 35 to 79) and 29% were HIV positive. The vast majority (89%) of HIV-positive men were taking antiretroviral therapy. This treatment was achieving good control of HIV, with 84% having an undetectable viral load and 83% a recent CD4 cell count above 350 cells/mm³.

At baseline, 51% of men were infected with an HPV type covered by qHPV and two-thirds with a strain preventable with nHPV. The most common HPV type was HPV16 (the most common HPV type associated with anal cancer), which was detected in 30% of participants.

Over the three years of the study, there was a high incidence of cancer-associated HPV types.

A fifth of men each year became newly infected with a strain of HPV covered by qHPV and 27% with a type covered by nHPV.

The HPV type commonly associated with genital warts (HPV6) was the most commonly detected type in new infections (9 per 100 person-years), followed by two high cancer-risk HPV types, HPV45 (8 per 100 person-years) and HPV16 (5 per 100 person-years).

Infection with HIV was a risk factor for the presence of high-risk HPV types at baseline (p = 0.002) and incident infections during follow-up (p = 0.033). There were no significant associations with age.

The investigators therefore conclude that there is a high prevalence and incidence of HPV strains covered by both HPV vaccines among older gay men, especially among men with HIV. They believe their findings could have implications for vaccination strategies as “prophylactic qHPV and nHPV vaccination of older homosexual men would prevent future HPV-associated disease”.