Harvard Health Letters

Q. My 14-year-old granddaughter has just completed her third injection of the Gardasil vaccine. I know it's designed to protect her from cervical cancer caused by a virus. But men can get the virus, too. Should my grandson also get the vaccine?

A. The virus in question is called human papillomavirus, or HPV. There are over 100 strains of HPV. About 40 of these strains can be transmitted by sexual contact. So-called low-risk strains cause genital warts (condylomas), but high-risk strains can cause cancer.

About 10,000 American women develop cancer of the cervix each year; nearly all cases are caused by HPV. High-risk strains of HPV can also cause cancer in men, but these malignancies are uncommon. Invasive cancer of the penis is diagnosed in fewer than 1,000 men a year; not all cases are associated with HPV, and the disease is especially rare in men who've been circumcised. Fewer than 1,500 cases of anal cancer are diagnosed in American men annually. Some are caused by HPV; most occur in gay men who practice receptive anal intercourse, and many patients also have immune systems that have been weakened by HIV infection. High-risk strains of HPV have also been linked to oral cancer.

Low-risk strains of HPV cause genital warts, which are soft, moist, fleshy growths on the genitals or nearby tissues. Doctors can administer local treatment to clear up genital warts, but the virus can persist in the body for up to two years, or sometimes longer.

HPV is very common; the CDC estimates that about 20 million Americans, mostly between the ages of 15 and 50, are currently infected. Most people with HPV don't know they have it but can still transmit the infection to their sexual partners. Safer sexual practices can reduce the risk of infection, but since condoms don't cover all potentially infected tissues, protection is incomplete.

In 2006, the U.S. Food and Drug Administration approved Gardasil for girls and women between the ages of 9 and 26 years. The vaccine contains two low-risk strains (HPV 6 and 11) and two high-risk strains (HPV 16 and 18) that account for 70 percent of cervical cancers and 90 percent of genital warts. The goal is to vaccinate girls at a young age before they become sexually active and acquire HPV.

Gardasil was first approved for use in boys in Europe and Australia, and the FDA followed suit in October 2009. But because the stakes are lower for males than females, the authoritative Advisory Committee on Immunization Practices has listed Gardasil as optional for boys but strongly recommended for girls and young women.

New vaccines are being developed, but even with a vaccine, men and women should also remember to prevent HPV the old-fashioned way.

-- Harvey B. Simon, M.D., Editor, Harvard Men's Health Watch

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