A vaccine from GlaxoSmithKline successfully blocks the virus that causes most cases of cervical cancer, the U.S. Food and Drug Administration said Friday.

In documents posted online, the FDA said Cervarix — Glaxo's vaccine against human papilloma virus or HPV — successfully blocked the two most cancerous strains of the virus nearly 93 per cent of the time.

The main study of the vaccine enrolled more than 18,000 women who either received Cervarix or a sham treatment. The FDA said the vaccine appears to fight HPV for more than six years, based on company data. Side-effects were minor, such as pain and swelling at the injection site.

The agency will ask a panel of vaccine experts next week whether Cervarix should be approved for girls and women ages 10 to 25. The FDA is not required to follow the group's advice, though it usually does.

A positive review from the agency will clear the British drug company's vaccine to compete in the U.S., though it could face an uphill battle against Merck's vaccine Gardasil, which has been on the market in the U.S. and Canada since 2006.

Besides having a three-year head start, Gardasil also defends against two more HPV types that cause 90 per cent of genital warts, something Cervarix does not target.

Cervarix already is approved in nearly 100 other countries, but has been delayed in the U.S. since 2007 when the FDA said it needed additional data. It is not approved in Canada.

Data needs review

Earlier studies of Cervarix showed a higher number of muscular and neurological problems among patients who used the vaccine compared with the alternate treatment.

The FDA said Friday it asked outside experts to examine more recent data from the company to see if Cervarix could have caused those problems.

"The conclusion in the case of each of these efforts was that the data are not sufficient to establish a link," the agency said in its review.

The FDA said it would ask Glaxo to report any continuing problems in a followup study planned for after the vaccine's launch.

About six million people in the U.S. each year contract HPV, which usually causes no symptoms and clears up by itself. While there are about 40 strains of the virus that are spread through sexual contact, only about 15 cause cancer in men and women.

Last year nearly 4,000 women died in the United States of cervical cancer.

Public Health Agency of Canada estimated that in 2008, 380 Canadian women would from it.

The incidence rate has declined by about two per cent per year between 1996 and 2005, a drop most likely related to greater Pap screening among young females, the Canadian Cancer Society said in its 2009 report on cancer statistics.

"Protection against cervical cancer is a very important health need for girls and young women, and we believe Cervarix has an important role to play in addressing this," said Glaxo spokeswoman Lisa Behrens.