experimental vaccine for preventing cervical cancer generally appears to be safe and effective, according to a report by staff members of the Food and Drug Administration.
The FDA staffers raise a few questions about the company-sponsored studies supporting the vaccine, which is called Gardasil. It could become the first government-approved measure against human papillomavirus, or HPV, which can cause cervical cancer and genital warts.
The FDA report was issued a day before a panel of outside experts is due to review the vaccine. FDA staff members routinely issue reports before FDA advisory panels meet, providing data analyses and offering questions to committee members. The FDA isn't bound by its advisory panels' recommendations, but it usually follows their advice.
The Merck vaccine is aimed at four types of HPV, including two that account for more than 50% of cervical cancer cases. The FDA says there are more than 15 types of HPV that can cause cervical cancer.
In the U.S., Merck appears to be leading
, which is developing an HPV vaccine called Cervarix. The British drug giant expects to submit its application by the end of the year.
GlaxoSmithKline filed a Cervarix application with the European Union in March. Cervarix targets the two biggest cervical cancer-causing types of HPV.
The Gardasil application has attracted attention on Wall Street, where analysts say the vaccine could eventually become a billion-dollar product. Gardasil was cited by Standard & Poor's earlier this year in its Top Ten list of important drugs to watch in 2006. GlaxoSmithKline has forecast that the worldwide market for HPV vaccines could be worth $4 billion to $7 billion by 2010.
In the U.S., the Food and Drug Administration says there will be an extra 9,710 cervical cancer cases and 3,700 cervical cancer deaths this year. Merck estimates that 20 million American men and women are infected with HPV, although the virus goes away on its own for most people.
HPV is more prevalent and more dangerous in developing countries. Worldwide, Merck says cervical cancer kills 300,000 a year.
Reviewing the Data
Merck's application to the FDA includes a pair of late-stage clinical trials comparing Gardasil to placebo. In one study, more than 12,100 women were tested; in the other, more than 5,700 were enrolled.
The FDA staff report says serious adverse events -- deaths, injury, side effects -- for Gardasil recipients "did not demonstrate a safety signal of concern."
However, the report cites two "important concerns" based on a review of the clinical trials. One was the possibility that Gardasil could "enhance disease" among a small group of patients who entered one of the clinical trials with a "persistent" HPV infection. The other concern was whether patients infected with types of HPV not covered by Gardasil could diminish the vaccine's efficacy.
These observations could be affected by the staff's looking at a small subgroup of patients in one clinical trial "who might have had enhanced risk factors," the report says. Although this one subgroup "remains a concern of the clinical review team," the staff concludes that "there is some evidence" that the Gardasil recipients "had more risk factors."
The staff adds that "there is compelling evidence that the vaccine lacks therapeutic efficacy" among women who have been exposed to HPV and whose infection remained when they entered the clinical trial. These women represented 6% of the total group.
By early afternoon, Merck's stock was off 31 cents to $34.81.