Yesterday, GlaxoSmithKline (NYSE:GSK) announced that its human papillomavirus (HPV) vaccine, Cervarix, received a positive opinion from the European Union medical authorities.

The positive opinion for a drug in the EU always precedes final regulatory approval, which should happen for Cervarix in the next several months. Following approval, GSK will then negotiate reimbursement within the individual EU countries, so sales should begin ramping up around the start of 2008. Cervarix is also awaiting regulatory approval in the U.S. after GSK filed a marketing application in March.

GlaxoSmithKline rival Merck (NYSE:MRK) received U.S. and EU marketing approval for its HPV vaccine, Gardasil, back in June and September of last year, respectively. Sales of the compound were $235 million for all of 2006 and jumped to $365 million in the first quarter of this year.

Merck's and GSK's vaccines are different, and each has its own advantages. Gardasil is effective against the HPV strains that cause genital warts, whereas Cervarix may confer a longer period of protection versus Gardasil for the two main strains of HPV that cause approximately "70% of HPV-related cervical cancer cases."

GSK is testing Cervarix against Gardasil in a phase 3 study to see which one will perform better over time in protecting women against the main cancer-causing HPV strains. Success in this study, which will take several years to complete, would be very good for marketing purposes -- although it won't be anything close to a conclusion to the vaccine wars, which are just about to heat up.

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Fool contributor Brian Lawler does not own shares of any company mentioned in this article. GlaxoSmithKline is an Income Investor recommendation. The Fool has a disclosure policy.