Merck’s AIDS vaccine fails in Experiment

24 September, 2007

In a huge and disappointing setback, a promising experimental vaccine for acquired immune deficiency syndrome (AIDS) vaccine failed to work in a large international test, leading the developer, Merck and Company, to halt the study.

Merck and Company, based in Whitehouse Station, New Jersey, the United States, has announced that it is ending enrollment and vaccination of volunteers in the study, which was partly funded by the National Institutes of Health of the United States.

Merck’s failure happens to be a high-profile one in the daunting quest to develop a vaccine to prevent AIDS. The company’s vaccine was the most advanced as of date, and was closely watched by experts in the field.

Officials at the company said 24 of 741 volunteers who got the vaccine in one segment of the experiment later became infected with human immonodeficiency virus (HIV), the virus that causes AIDS.

In a comparison group of volunteers who got dummy shots, 21 of 762 participants also became infected.

Keith Gottesdiener, head of Merck’s clinical infectious disease and vaccine research group, said: “It is very disappointing news. A major effort to develop a vaccine for HIV really did not deliver on the promise.”

The volunteers in the experiment were all free of HIV at the start. But they were at high risk for getting the virus – most were homosexual men or female sex workers. They were all repeatedly counseled about how to reduce their risk of HIV infections, including use of condoms, according to Merck.

In a statement, the National Institutes of Health said that a data safety monitoring board, reviewing interim results, found the vaccine did not prevent HIV infection. Nor did it limit severity of the disease “in those who become infected with HIV as a result of their own behaviors that exposed them to the virus” – another goal of the study.

Merck’s was the first major test of a new strategy to prevent HIV infection. The first wave of attempts to develop a vaccine tried to stimulate antibodies against the virus, but that has not worked so far.

The new effort, which is being tried in most other current research, is aimed at making the body produce more of a crucial immune cell called killer T cells. The goal is to “train” simultaneously those cells, like an army, to recognize quickly and destroy the AIDS virus when it enters cells in the bloodstream.

Some researchers still are working on vaccines to neutralize the AIDS virus.

Merck and the HIV Vaccine Trials Network, an international collaboration of researchers and institutions funded by the National Institutes of Health, co-sponsored the study.

The experiment, called STEP, began in December 2004 and had enrolled 3,000 volunteers in Australia, Brazil, Canada, the Dominican Republic, Haiti, Jamaica, Peru, Puerto Rico and the United States.

The results announced on September 21, 2007, involved volunteers whom researchers thought would benefit most because they had never been exposed to the particular cold virus used in the vaccine.