Network nixes wide-scale AIDS vaccine trials

SEATTLE, Washington (CNN) -- A government clinical and research network has nixed plans to begin a large-scale AIDS vaccine trial, a top official with the National Institutes of Health said Sunday.

The HIV Vaccine Trials Network had planned to test two AIDS vaccines in combination -- VaxGen's AIDSVAX and another investigative vaccine called ALVAC, made by Aventis Pasteur -- to determine whether they would prevent HIV infection.

The vaccine combination had undergone two trials -- Phase I tests on a small number of volunteers for safety alone and Phase II tests, which utilize more volunteers and begin to gauge the vaccines' effectiveness. Each phase can take several years to complete.

But in study results presented Sunday, ALVAC's performance did not persuade government officials to approve a Phase III trial, the last stage before a company can apply for approval by the Food and Drug Administration.

In the planned trial, thousands of healthy people at risk for infection with HIV, the virus that causes AIDS, would have been tested over several years.

Researchers are currently conducting phase I and II trials on roughly 20 AIDS vaccines. But only one vaccine, AIDSVAX, has reached phase III status.

The vaccine combination under consideration Sunday ideally would create a double safety net by targeting the virus before it enters human cells and going after viruses that slips past the first barrier and into the cells.

AIDSVAX is tailored to teach the immune system to recognize the virus as an enemy and attack before it enters the cell. ALVAC, meanwhile, uses a harmless bird virus to get small pieces of HIV into human cells, where they theoretically would be destroyed by the immune system.

Volunteers were to get the ALVAC to prime the immune system and then AIDSVAX as a booster, similar to booster shots given to children after many immunizations. The U.S. Army has nearly completed a similar Phase II trial in Thailand.