Trials of a new HIV vaccine come to an abrupt halt

Sep 24 2007

Trials of a new HIV vaccine have come to an abrupt halt after it did not prevent volunteers from becoming infected.

The HIV vaccine had looked promising but the Phase II clinical trials were stopped after it was found to be ineffective in preventing volunteers who were at high risk for acquiring HIV from becoming infected.

This is a disappointment as the vaccine, known as V520, was the result of ten years work.

Previous experiments on animals and people had been promising enough to encourage the development and the conducting of the tests.

The STEP trial had been sponsored by the manufacturer Merck along with the HIV Vaccine Trials Network, which is financed by the NIAID (National Institute of Allergy and Infectious Diseases).

The STEP trial, included 3,000 healthy volunteers from a variety of backgrounds, aged 18-45 mainly from Latin America, the United States, Australia and the Caribbean; the volunteers received three doses of the vaccine over a period of six months.

According to the Merck, in one placebo group of 762 volunteers 21 became infected with HIV, while in another group of 741 who received the experimental drug, 24 became infected with HIV.

The STEP Independent Data Safety Monitoring Board then decided that the human trial was doomed to fail.

The vaccine was made up of a common cold virus which had copies of three HIV genes and the theory was that when volunteers were exposed to the genes an immune response would be triggered known as cell-mediated immunity, which would protect them from HIV infection.

The apparent ability of the vaccine to turn on the immune system, led many to regard the vaccine with optimism in that it might lead to new developments.

But the vaccine failed to prevent infection, and also failed to reduce levels of the virus in the bloodstream of people who became infected so the trial was abandoned.

Dr. Anthony S. Fauci, the director of the National Institute of Allergy and Infectious Diseases, says the results are obviously disappointing but Merck has promised to reveal all the information it has collected with scientists.