WASHINGTON (AP) — A panel of federal experts will consider Wednesday whether GlaxoSmithKline's long-delayed vaccine Cervarix should be approved in the U.S. to prevent cervical cancer in women, even as competitor Merck requests expanded use of its vaccine for boys. London-based drugmaker Glaxo has already won approval for its vaccine in Europe, but its U.S. launch was delayed in 2007 when the Food and Drug Administration said it needed more data about the vaccine. The FDA last week said more recent data submitted by Glaxo show the vaccine appears safe and blocks two strains of a virus that cause most cases of cervical cancer. The human papilloma virus, or HPV, infects about 6 million people in the U.S. each year, and is mainly spread through sexual contact. It usually causes no symptoms and goes away within two years, though rare cases can develop into warts and cancers in both men and women. On Wednesday, the agency's outside panel of vaccine experts will consider whether Cervarix should be approved for the U.S market. The FDA is not required to follow the group's advice though it usually does. Even if the FDA grants approval, Glaxo will face an uphill battle against Merck's Gardasil, which has had the U.S. market to itself for the last three years. Besides an established brand, Gardasil also boasts an extra degree of protection against sexually transmitted diseases. Merck's vaccine defends against two other HPV types that cause 90 percent of genital warts, something Cervarix does not target. Leerink Swan analyst Seamus Fernandez estimates Glaxo's Cervarix will take 25-30 percent of the U.S. market for HPV-blocking vaccines. Even as the British drugmaker moves closer to competing in the U.S., Whitehouse Station, N.J.-based Merck is poised to begin marketing Gardasil to boys and men. In a separate review last week, the FDA said that vaccine prevented genital warts in males 90 percent of the time. Merck will ask FDA to approve the vaccine for boys and men ages 9 to 26. The vaccine already is approved to treat females in that age range. While an approval decision could theoretically double the market opportunity for Gardasil, analysts don't expect major use among boys and men. Genital warts caused by HPV usually clear up by themselves, and the cancers caused by the virus are extremely rare in men. Fernandez estimates sales to males at $200 million to $300 million, out of total Cervarix sales of $1.65 billion by 2015. Last year, Cervarix sales totaled $231 million, compared with $1.4 billion for Merck's Gardasil.