I was catching up again on my favorite periodical (Morbidity and Mortality Weekly Report—the Dengue Fever story is Awe.Some.) I came across the official recommendations for Gardasil for males. Gardasil is the vaccine produced by Merck that can protect women against infection by four strains of human papilloma virus (HPV). The vaccine has been shown to prevent genital warts and pre-cancerous lesions caused by the virus. The vaccine, in conjunction with Pap tests, has the potential to significantly reduce the incidence of cervical cancer.
Of course, HPV infections do not arise spontaneously on the female cervix. In heterosexuals, HPV is passed between male and female partners, but men, not having a cervix, do not suffer the same consequences. They do, however, get genital warts and sometimes develop penile, anal, and oral cancers due to HPV. Men who have sex with men are at even higher risk than men who strictly have sex with women.
So there are several potential advantages to vaccinating men against HPV: it can protect them against genital warts and certain cancers; and it can protect their partners. In October of 2009, the FDA approved the HPV vaccine for use in males. An analysis by the Advisory Committee on Immunization Practices (ACIP) published in a recent MMWR gives us some guidance into the use of the vaccine in males.
Studies show that the HPV vaccine is very effective at preventing genital warts in vaccinated men. In addition, vaccinated males were found to have a good antibody response to the vaccine. The ACIP did some mathematical modeling to assess the affect of vaccination on the overall population burden of HPV disease. They found that if greater than 80% of females were vaccinated, the cost/benefit ratio of vaccinating males was not terribly favorable. When fewer than 80% of females are vaccinated (which is the current case), there may or may not be a cost/benefit advantage to vaccinating males. Because of this, one recommended strategy for addressing the societal burden of HPV disease is to improve vaccination rates in females, who suffer the higher burden of this infection.
Using the data, they came up with a recommendation of optional vaccination of young males to reduce their personal risk for genital warts. After formulating their recommendations, further data has become available showing that the shot is very effective at reducing precancerous anal lesions in men who have sex with men. I would argue that this group should also be targeted for vaccination.
In sum, the data show that Gardasil is effective in females. They also show that it is effective at preventing genital warts in all men, and probably in preventing anal cancers in men who have sex with men. Given that men are usually the source of infection in women, we should keep an eye on the data and on the cost of vaccination to see if more widespread vaccination of males would be appropriate.