Phase 2 clinical trials of Merck's (NYSE:MRK) HIV vaccine, created using the same virus that causes the common cold, were frozen on Friday.

The vaccine is essentially a cold virus modified to contain three proteins from HIV. It was hoped that the vaccine would cause the patients' immune system to create antibodies against HIV. Unfortunately, that doesn't seem to have occurred. The vaccine joins VaxGen's HIV vaccine, which failed in 2003, in the looked-promising-but-failed category.

An independent data-monitoring board stopped all clinical trials associated with the vaccine after an interim analysis concluded that the vaccine failed to keep subjects from being infected with HIV through behaviors that exposed them to the virus. The vaccine also failed to lower the amount of virus in the subjects after being infected, which was a secondary endpoint of the study.

Merck's vaccine was furthest along in clinical trials, but its failure opens up the door for other drugmakers that have vaccines in early trials, including Sanofi-Aventis (NYSE:SNY), Novartis (NYSE:NVS), and Wyeth (NYSE:WYE). The first company to launch a successful HIV vaccine should have an instant blockbuster on its hands, as a vaccine is probably the only feasible way to fight AIDS in developing countries.

While a successful trial would have been great news for Merck, it's still doing quite well in the HIV market. The company still has two HIV-fighting drugs, Crixivan and Stocrin, that combined for $75 million in sales last quarter. In addition, an FDA advisory committee unanimously recommended approval of its newest drug, Isentress. If it is approved, sales of that first-in-class drug might be slow to start but should increase as more patients become resistant to the currently available drugs.

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Fool contributor Brian Orelli, Ph.D., doesn't own shares of any company mentioned in this article. The Fool has a disclosure policy.