UPDATE 3-US FDA staff: GSK HPV shot works, miscarriages seen

* Studies show vaccine fights cervical cancer virus - FDA

* FDA staff: More miscarriages seen in Cervarix patients

* Serious events similar overall with another shot - FDA

* Advisory panel to weigh Cervarix on Wednesday

* Glaxo shares up 1 percent (Adds analyst comment)

By Lisa Richwine

WASHINGTON, Sept 4 (Reuters) - A proposed GlaxoSmithKline Plc (GSK.L)(GSK.N) vaccine protected women and teenage girls from the virus that causes cervical cancer but more miscarriages were reported than with another immunization, U.S. reviewers said in documents released on Friday.

Food and Drug Administration staff also said a rival vaccine that is already on the U.S. market, Merck & Co Inc's (MRK.N) Gardasil, was safe and effective for boys and young men. [ID:nN04128003]

Both vaccines aim to protect against diseases linked to the sexually transmitted human papillomavirus (HPV), which causes cervical cancer, genital warts and penile and anal cancers.

FDA reviewers said a Glaxo study of more than 18,000 females showed the company's Cervarix vaccine prevented precancerous lesions associated with two HPV strains in girls and women ages 15 to 25.

The rates of serious health problems were similar overall between people given Cervarix compared with a hepatitis A vaccine, the agency staff said.

FDA reviewers also said an independent analysis concluded data "do not establish a causal relationship" between a higher rate of miscarriages reported among females given Cervarix. The findings, however, "were insufficient to rule out a small effect in pregnancies conceived in the three months immediately after vaccination," reviewers said.

The vaccine is not intended for pregnant women, and females in the study were advised to abstain from sex or use birth control for up to two months after getting the shots. Cervarix is given in three doses over six months.

Glaxo spokeswoman Lisa Behrens said the miscarriage cases were "rigorously assessed" and "do not suggest a causal relationship."

FDA reviewers said they will ask an advisory panel that meets Wednesday about the miscarriages and other issues as the agency decides whether to approve Cervarix for sale. The committee of outside experts also will consider whether to urge clearance of Merck's Gardasil in men and boys.

The FDA usually follows panel recommendations.

Morgan Stanley analyst Andrew Baum said the FDA's stance on Cervarix was "favorable" and the product appeared set to win approval. He said he expected Merck to lose more than 25 percent of its market share to Cervarix.

Glaxo is counting on Cervarix to drive future growth in its vaccines unit, a priority area for the company. Cervarix is approved in 98 countries, but its approval stalled in the United States after Glaxo's initial application in 2007. Its rival, Gardasil, won U.S. clearance in 2006.

FDA staff said one of the main issues with Cervarix in 2007 was cases of neurological and muscle-related problems that could have been caused by autoimmune reactions. Agency reviewers analyzed additional findings and found "data are not sufficient to establish a link," the staff summary said.

Information on those problems will be collected in a post-approval study, and a registry to follow pregnancies and miscarriages also will be established, the agency said.

Glaxo "recognizes the need for close monitoring of pregnancy-related events in ongoing clinical trials" and will monitor the issue in a registry, spokeswoman Behrens said.

Some analysts say the U.S. delay will make it tough for Cervarix to compete against Gardasil. The Merck vaccine had global sales of $1.4 billion in 2008, compared with 125 million pounds ($204 million) for Cervarix.

Cervical cancer can be caught early through Pap smears, and treated. Still, about 4,000 U.S. women die each year from the disease. Worldwide deaths from the disease total about 280,000, mostly in developing countries where screening is lacking.

Glaxo shares rose 1 percent to $39 on the New York Stock Exchange. (Reporting by Lisa Richwine; Editing by Andre Grenon, Gary Hill)