More than 100 types of human papilloma virus (HPV) are known to exist. More than 30 types of HPV are transmitted through sexual contact. At least 19 types of HPV cause cervical cancer in women and also cause cancer of the vagina, vulva, penis, anus and certain types of throat cancer.

Recently, the U.S. Food and Drug Administration approved a vaccine called Gardasil, made by Merck & Co., for the prevention of infection by four types of HPV. Gardasil prevents infection by two cancer-causing HPV types (16 and 18 - responsible for 70% of cervical cancer in the United States) and two HPV types that cause genital warts (6 and 11 - responsible for about 90% of the HPV-induced genital warts in the United States).

A competitor of Merck, GlaxoSmithKline, has a vaccine under review by the FDA that they hope to have approved in the near future. This vaccine, called Cervarix, prevents infection with HPV types 16 and 18.

The FDA approved Gardisil for use in girls and women between the ages of 9 and 25 who have not ever been exposed to HPV. The CDC's Advisory Committee on Immunization Practices recommends vaccination of girls at the ages of 11 or 12.

Both Gardisil and Cervarix are almost 100% effective against the virus types they contain, but are probably ineffective against all the strains they do not contain. How long the protective effect of either HPV vaccine lasts after inoculation is unknown, but many experts believe resistance to infection will last at least four years.

Even though the current HPV vaccine only protects against a limited number of HPV types, in the U.S. it makes sense for young women and girls to be vaccinated since the risk of injury and death from HPV infection is so high. The vaccine has very few side effects, and medical experts believe the risk of vaccination is extremely low in comparison to the benefit.

While some religious leaders are opposed to vaccination because they are worried that it will encourage sexual promiscuity, this "virginity or death" stance has no legitimate place in a civilized society. On the other hand, it makes little sense for politicians to force girls to be vaccinated since the commercial vaccine, while very profitable to its manufacturer, is only the beginning of the solution to worldwide HPV prevention.

The new HPV vaccines are clearly important medical progress in controlling life-threatening viral infections, but problems remain. If only females are vaccinated, the HPV reservoir in males will be unaffected and the threat to the human population as a whole is unlikely to be reduced. With HPV infections so high worldwide, it is likely that other HPV strains not included in the commercial vaccines will increase in frequency over time, leaving even vaccinated people susceptible.

From the standpoint of worldwide virus control, the high cost of the vaccine makes it too expensive for use in developing countries. Ongoing research should improve the breadth of effectiveness of HPV vaccines to include protection against essentially all virus strains. In addition, in the future there may be therapeutic vaccines to treat people already infected with HPV. For now, keep informed, remain skeptical of commercial advertising and unproved claims, but take advantage of this valuable advance in preventative medicine.