By Nicola Jones

Ever since Gardasil, made by Merck, landed on the market in 2006 for protecting women under 27 from the human papillomavirus (HPV), the drug giant has aimed to expand the vaccine’s label to older women. But conflicting regulatory decisions are highlighting a debate about whether the vaccine is worth approving for use in an older cohort.

Merck’s vaccine (and its competitor, GlaxoSmithKline’s Cervarix), immunizes against a handful of HPV strains, dramatically reducing the occurance of the genital warts and cellular abnormalities that can precede cervical cancer for four years or more after immunization. Gardasil has been approved for years for use in dozens of countries around the world: the US Food and Drug Administration (FDA) approved the jab for girls and women aged 9–26 in 2006. But even though many nations have approved the use of Gardasil in older women up to age 45—including countries overseen by the European Medicines Agency and, just a month ago, Canada—the FDA ruled against this expansion in April.

There is no question that the vaccine is safe and can work in older women. But there is also no question that it will have less impact in that group, because the vaccine only works well for those who have not been exposed to the HPV strains previously. “Once you start having sex, you’re going to have an HPV infection,” says epidemiologist Abby Lippman of McGill University in Montreal.

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Image: Flickr user Eugene Peretz, under Creative Commons