monday after federal regulators pledged to give a

CSL related.

VaxGen said the Food and Drug Administration had agreed to give an expedited review to two of its experimental vaccines to combat HIV, the virus that causes AIDS.

The FDA grants "fast-track" status to vaccines or medications if the products are for life-threatening illnesses and "address unmet medical needs." Under the fast-track process, the FDA typically decides on a marketing application six months after it's filed. A standard review generally takes 12 to 18 months.

The fast-track designation doesn't guarantee approval. VaxGen has long faced doubts about whether its vaccine can gain marketing clearance. Reflecting that skepticism, the company's stock is a favorite among short sellers, who profit if the share price declines.

On Friday, VaxGen's shares plunged after an article in Nature, one of the most prestigious science journals in the world, raised questions about whether the type of vaccine VaxGen is developing would be effective against HIV.

Developing an AIDS vaccine is considered enormously difficult because the virus is so quick to mutate.

Of all the efforts to develop an AIDS vaccine, VaxGen's program is believed to be the furthest along, having reached late-stage patient testing. No. 2 U.S. drugmaker Merck & Co. (MRK: news, board) as well as other companies are also working on AIDS vaccines.

A spokesman for VaxGen, which is based in Brisbane, Calif., said Monday the company remains "optimistic" that AIDSVAX, as the vaccine is known, will be effective. But the spokesman, Jim Key, acknowledged that VaxGen wouldn't know for sure until it has had a chance to analyze results from late-stage, or Phase III, trials. Key said VaxGen plans to announce the results in the first quarter.

Although its effectiveness remains in question, the AIDSVAX appears to have a strong safety profile. The vaccine is designed so that it can't cause HIV infection, according to VaxGen. Vaccines for other diseases have in some instances been known to actually cause the disease they are supposed to prevent. Merck & Co., Inc. (NYSE : MRK) Last Trade: 3:50 PM EST

Last Sale 58.51
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