The HPV Vaccine Works Best Before Exposure
During a week in which Texas Gov. Rick Perry stepped back from his position that girls should be required to have the human papillomavirus (HPV) vaccination, the New England Journal of Medicine has published new evidence that the vaccine is most effective at preventing cervical cancer when it's administered to girls before they become sexually active.
Cervical cancer, a major killer worldwide, has been significantly reduced in the United States because of the introduction of the pap test, which has cut the number of deaths by three quarters since the 1950s. According to the American Cancer Society, about 3,670 Americans now die each year of cervical cancer. Two strains out of more than 100 HPV types, types 16 and 18, cause 70 percent of cervical cancer cases.
The new study followed 12,167 women from 13 countries for three years who had either received the HPV vaccine, Gardasil, or a placebo. For women who had not previously been exposed to the key HPV types, the vaccine was 98 percent effective at preventing precancerous cervical lesions. Among all study participants, including women who might have been previously exposed to HPV by being sexually active, the vaccine was only 44 percent effective.
"Once you get into populations that have been infected with one or more HPV types, you see a lower level of protection," says Laura Koutsky, an epidemiologist at the University of Washington, who chaired the committee that oversaw the research.
A second study came to similar conclusions about the vaccine's ability to prevent genital warts and other HPV-related conditions.
Koutsky points out that the vaccine Gardasil–which is FDA approved, available, and recommended by the Centers for Disease Control and Prevention for preadolescent girls–does not guarantee protection from cervical cancer. That's because 30 percent of cervical cancer cases are caused by strains not included in the vaccine. Plus, it's unclear how long the vaccine remains effective. The vaccine costs about $360 and requires three shots over six months.
Meanwhile, the debate over requiring HPV vaccination remains extremely contentious. Social conservatives fear that a vaccine for a sexually transmitted disease will promote promiscuous sexual behavior. There's also concern that wide-scale vaccination programs are expensive and that Merck, the vaccine's maker, is pushing the drug onto the public too quickly.
Governor Perry made headlines in February when he issued an executive order requiring that sixth-grade girls in Texas be vaccinated by 2008. The order met stiff resistance from state lawmakers, who responded with a bill that would block mandatory vaccination for at least four years. On Tuesday, Perry announced he would not veto that bill.
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