May 18, 2006 -- Government advisors strongly backed U.S. approval of the first vaccine Thursday, saying it appeared highly effective in preventing the infection that causes it.
The vaccine, called Gardasil, was nearly 100% successful in protecting young women against new infections with two types of human papillomavirus (HPV), a common sexually transmitted virus known to cause cervical . These two types of HPV are responsible for 70% of cervical cancers.
Health groups called the vaccine a potential boon for preventing cervical cancer, which is expected to be diagnosed in 9,710 U.S. women this year and kill roughly 3,700.
But experts warned that the vaccine only offers protection for women who have not already been infected. HPV infection is quite common for men and women, and many people do not realize that they are infected. Also, cervical cancers are caused by other factors.
It suggests Gardasil is likely to have the most benefit only when given to adolescents before their first sexual intercourse, they said.
Still, a panel of FDA advisors praised Merck -- the maker of Gardasil -- for its study of the vaccine in approximately 27,000 women in 33 countries.
“This is certainly a wonderful, good step,” said Monica M. Farley, MD, the panel’s acting chair and a professor of medicine at Emory University in Atlanta.
The panel voted unanimously that the vaccine is safe and effective in preventing precancerous lesions in women between 16 and 26 years of age. Studies also suggested that it boosts HPV immunity in 9- to 15-year-olds, a group that would ultimately be the target of an effective immunization campaign, experts said.
Gardasil is given in a series of three injections over six months. Merck’s studies showed that the protocol prevented the development of precancerous lesions in 98% or more of women up to 3.5 years after vaccination -- as long as women were infection-free when they received it.
HPV types also causein both females and males. The vaccine contains two virus types blamed for most cases of the lesions.
But the vaccine doesn’t work against a virus already infecting the body. Its purpose is for prevention, not treatment. At the same time, there is no simple and cheap test for the presence of HPV infection. That means that many women who get the vaccine may already be carrying one of the several different types of HPV.
FDA scientists said their analysis showed that vaccination of unscreened women in doctors’ offices would likely cut the rate of precancerous lesions by 40%, since many are likely to already carry infections with one or more HPV types.
While praising its potential, several experts expressed concern that overconfidence in the vaccine could undo years of progress in promotingscreening in women using Pap tests. The tests are the only reliable way to detect the presence of abnormal cervical cells that may be cancerous or precancerous.
Eliav Barr, MD, Merck’s senior director for vaccines and biologics, pledged that the company would not promote Gardasil as an alternative to Pap testing. “This vaccine is not a replacement for cervicalscreening, and I think that that’s clear,” Barr said.
Experts also urged Merck and the FDA to conduct longer-term studies on Gardasil, because researchers still don’t know how long immunity will last.
“There are going to be questions of what lays down the line in the way of boosting requirements,” said Pamela McInnes, director of the Center for Integrative Biology and Infectious Diseases at the National Institutes of Health and a member of the FDA panel.
Barr said that the company planned to track thousands of Norwegian women who received the vaccine.
Merck is seeking to market the drug for HPV prevention in girls as young as 9 years old. The Advisory Committee on Immunization Practices, which advises the federal government on vaccination policies, is set to meet next month. The panel will likely consider whether HPV vaccine should be added to list of recommended and required childhood immunizations, Barr said.
News of the vaccine’s development has also prompted conservative Christian groups to question its potential to undermine abstinence messages by making sex less risky.
Peter S. Sprigg, vice president of the Family Research Council, called the potential marketing of Gardasil a “positive development.”
“But we would be concerned if this were administered with a message that, ‘Hey, it’s now save for you to have sex,’” he tells WebMD.