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GlaxoSmithKline PLC's (GSK) Cervarix vaccine induced a higher immune response in women against the virus that causes cervical cancer than Merck & Co.'s (MRK) Gardasil, according to a Glaxo-funded clinical trial.

However, the study didn't measure which vaccine was more effective at preventing actual cases of cervical cancer or pre-cancerous lesions - that would require a longer and larger trial. Both vaccines are designed to prevent infection by human papillomavirus, or HPV.

Nevertheless, U.K.-based Glaxo hopes the results, to be presented at a Swedish medical conference that begins Friday, will help give Cervarix a competitive edge if it reaches the U.S. market, which Merck has had to itself since Gardasil's launch in 2006. The U.S. Food and Drug Administration is reviewing Cervarix and could decide whether to allow it to go on sale by autumn. Cervarix is already on the market in other countries including the U.K.

"The study clearly shows a higher level of immune response in women receiving Cervarix than Gardasil," Gary Dubin, vice president of global clinical development in Glaxo's vaccine unit, told Dow Jones Newswires in an interview.

Before knowing the final data, a Merck executive played down the importance of comparing the vaccines' immune responses. "It's disease efficacy that's really the most important, and we certainly have very high efficacy against some very important disease endpoints," said Rick Haupt, program lead for HPV vaccines in Merck's research arm.

In clinical studies tested against placebo, Gardasil's efficacy rates approached 100% at preventing cervical cancer or pre-cancerous lesions that were caused by the four HPV types targeted by Gardasil. (However, there are other HPV types not targeted by Gardasil that can cause disease, and Gardasil isn't approved in the U.S. to protect against these types.)

Gardasil is marketed in most major European countries by Sanofi Pasteur MSD, a joint venture of Merck, Whitehouse Station, N.J., and France's Sanofi-Aventis SA (SNY).

Glaxo launched the head-to-head trial in the U.S. in 2007 in more than 1,100 women ages 18 to 45. The vaccines were given in three shots over six months. According to Glaxo, the women who received Cervarix had higher levels of "neutralizing antibodies," which help fight off cancer-causing HPV types, than Gardasil, one month after the last dose. For one type, the levels induced by Cervarix were more than twice as high as Gardasil and for another type they were more than six times higher, according to figures provided by Glaxo.

Glaxo said both vaccines had "acceptable" safety profiles, but rates of certain symptoms such as injection-site reactions were higher among Cervarix users. Both vaccines have been linked to headache and fainting.

The vaccines are designed differently. Cervarix has a proprietary additive known as an adjuvant, which Glaxo believes enhances its effectiveness, while Gardasil uses a more conventional adjuvant. Gardasil targets four HPV types including those that cause most cases of genital warts, while Cervarix targets two types and isn't intended to provide as much protection against warts.

Merck's Gardasil sales rose quickly after its 2006 U.S. launch but last year declined 5% to $1.4 billion as the company encountered difficulty convincing women ages 19 to 26 to get the shots. Gardasil sales recorded by Sanofi Pasteur MSD, however, jumped more than 70% to about $780 million.

Merck is trying to expand Gardasil's usage by seeking FDA approval for its use in women up to age 45 (it's now approved for 9- to 26-year-olds), and in males for the prevention of genital warts and rare cancers. Glaxo isn't seeking an indication in males.

Glaxo recorded $231 million in Cervarix sales last year.

Glaxo is set to present other data supporting Cervarix, including potential evidence that it offers some protection against additional HPV types, and that its immune-response levels last for at least 7.3 years after vaccination. Merck previously had data suggesting Gardasil could protect against additional HPV types but the FDA declined to incorporate this into the prescribing label.

Separately, Merck is presenting data showing an experimental precursor to Gardasil, a vaccine targeting just one HPV type, had sustained efficacy for an average of 8.5 years after vaccination. In another study, Gardasil reduced the number of abnormal Pap tests and subsequent procedures designed to ward off cervical cancer. Pap tests screen for cervical cancer.

-By Peter Loftus, Dow Jones Newswires; 215-656-8289; peter.loftus@dowjones.com

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