Why was the vaccine against the cancer-causing, sexually transmitted HPV virus not approved for men at the same time it was for women? Is there any reason to think that men and women would react to it differently?
Interesting question. First, a little background.
Gardasil is a genetically engineered vaccine to immunize girls and women ages 9 to 26 against four types of human papillomavirus (HPV). HPV is the name given to a family of viruses, many of which can be transmitted from one partner to another through sexual activity. HPV may represent the most frequent sexually transmitted infection in the United States. It is estimated that over 6 million people become infected by a sexually related form of HPV every year. Some estimates suggest that over half of all sexually active males and females become infected at one point or another in their lifetimes.
Certain types of HPV can sometimes evade the body's immune system and, when they do, establish a state of persistent infection. That in turn may cause certain cancers. Indeed, this is now recognized as the major cause of cervical cancer and related conditions, and vaccines that immunize people against HPV could make a dramatic impact against these diseases.
Gardasil is the first vaccine in the United States approved for the prevention of cervical cancer and precancerous cell abnormalities in the cervix and also certain precancerous conditions in the vagina and vulva. In addition, Gardasil prevents genital warts (technically called condylomata acuminata). However, Gardasil does not confer protection against HPV types other than those covered in the vaccine. Gardasil is expected to prevent up to 70 percent of cervical cancers, but the vaccine works for prevention only. It does not confer protection if the targeted HPV infection has already occurred, and on that count, it is not a treatment for a woman already infected.
The manufacturer is working with the Food and Drug Administration (FDA), seeking approval to expand the age range for vaccine use to include women ages 27 through 45. There is another similar but not identical vaccine against certain types of HPV, called Cervarix, which is approved for the prevention of precancerous cervical lesions and cervical cancer in certain countries outside the United States. Its manufacturer, GlaxoSmithKline, is working with the FDA to obtain approval for its HPV vaccine in the United States.
What about the Gardasil vaccine for boys and young men? Indeed, recently, the vaccine manufacturer announced that it was seeking FDA approval to use Gardasil to prevent genital warts and related conditions in males ages 9 to 26. There is no a priori reason to think the genders would react differently. If females and males are immunized, one would expect a reciprocal benefit to the population at large.
All in all, the development of an FDA-approved vaccine against HPV is a major milestone for public health. But there is an additional and worrisome turn of events in this story. Oral HPV infection is now believed to be a substantial risk factor for certain kinds of oropharyngeal cancers, that is, cancers that form in the middle portion of the throat, including the base of the tongue and, notably, the tonsils. This may partially explain why there is an increasing incidence of cancers in the tonsil and base of the tongue. One important research question is whether vaccines like Gardasil will have an impact on these trends.
HPV-associated oral carcinoma occurs to a higher degree in men and does so at a younger age and at a more advanced stage than non-HPV-associated oral carcinoma. Moreover, investigators from Johns Hopkins University and the National Cancer Institute recently published data suggesting that HPV-associated oropharyngeal cancer is associated with more than 25 lifetime sex partners and more than six lifetime oral sex partners. These studies and others like them provide yet another reason to consider HPV vaccination in both females and males, since oropharyngeal cancers occur in both. If vaccination is as effective in preventing oral HPV infection as it is in preventing infection of the cervix, one may someday see a significant decrease in the incidence of oropharyngeal cancer in vaccinated populations.
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