HPV vaccine effective.

An experimental vaccine is effective against a strain of the sexually transmitted human papilloma virus (HPV)--Type 16--that causes about half of all cases of cervical cancer, a recent U.S. study has found.

Researchers predict that, if confirmed by additional testing to be safe and effective, the vaccine could reach the market in about five years, being given in three shots over six months.

Although more than 30 types of HPV infect human genitalia, not all cause cervical cancer. And, while infection with HPV is common among sexually active individuals, more than 90 percent of HPV infections are either naturally eliminated or suppressed by individuals' immune systems. However, the infection persists in some women and causes cervical lesions. Most lesions go away, but some develop--usually over about 20 years--into cervical cancer. The disease kills about half of some 450,000 women throughout the world who develop it each year. It is also the leading cancer killer of women in the developing world, where Pap tests to detect cervical abnormalities are not routinely available.

The study was conducted by U.S.-based Merck Research Laboratories, a unit of Merck & Co., Inc., which developed the vaccine and funded the research, and by the University of Washington among 2,392 women ages 16 to 23 years at 16 U.S. sites. Of 1,533 women included in the final data analysis, none of the 768 women who received three doses of the vaccine became infected with HPV-16 or developed precancerous lesions. In contrast, 41 of the 765 women who received injections of placebo instead of the vaccine developed persistent HPV infections, and nine developed precancerous lesions. Women receiving the vaccine experienced no serious vaccine-related adverse effects.

The results, reported November 20, 2002 in the New England Journal of Medicine, describe the outcome for women followed for 17 to 27 months (median of 17.4 months), but the study will continue until the women have been tracked for four years.

How long the protection afforded by the HPV vaccine may last is unknown. Whether any vaccine can completely protect against cervical cancer is also unclear, since cervical cancer is caused by more than 20 types of HPV (primarily types 16, 18, 31, 33, and 45). Thus, regular Pap smears to detect cervical cancer will probably remain necessary even for vaccinated women. Furthermore, there is no evidence that the vaccine under development can reverse infection or eliminate cervical lesions once they have developed.

However, other adverse reproductive health effects caused by HPV infection--such as genital warts and rare forms of penile, anal, and oral cancer--might be prevented by such a vaccine. The vaccine now being developed and tested by Merck would immunize patients against both HPV-16 and HPV-18 (which causes another 20 percent of cervical cancers), as well as HPV-6 and HPV-11, which cause about 90 percent of genital warts. Because some HPV-infected men develop genital warts, they may have an incentive to be vaccinated and, consequently, would not transmit the virus to their sexual partners.