Volunteers from four different continents were enrolled in these trials that were halted last September because the initial results showed that instead of protecting the recipients of the vaccine, the drugs were actually increasing the risk of HIV infection.
In a setback that is being called a catastrophe by experts, two field tests, human trials, to test AIDS vaccines, have been halted after it was discovered that the vaccine not only didn't protect people but increased the risk of becoming infected.
The recently closed studies, STEP and Phambili, used the same vaccine -- made from a common respiratory virus called adenovirus type 5 that had been crippled and then loaded with fragments of HIV. Both studies were halted when it became clear the STEP study was futile and possibly harmful.
The results of the Phambili vaccine trial, which was conducted in South Africa, were revealed last month and only worsened the gloom. Although the number of new HIV infections in that study was far smaller than in STEP -- and too few to draw firm conclusions from -- those results, too, hinted at a trend toward harm among vaccine recipients.
The STEP and Phambili trials were funded by the National Institutes of Health, which for this fiscal year had a budget for AIDS vaccine research of $497 million.
The NIH is meeting next week to reassess the AIDS vaccine program but some respected experts have already made up their minds.
For example, Ronald C. Desrosiers, a molecular geneticist at Harvard University, spoke at an AIDS conference last month as said, "None of the products currently in the pipeline has any reasonable chance of being effective in field trials. We simply do not know at the present time how to design a vaccine that will be effective against HIV."
Another expert, Robert Gallo, co-discoverer of the human immunodeficiency virus (HIV), which causes AIDS, and head of the Institute for Human Virology in Baltimore, describes this latest failure as a catastrophe and says, "This is on the same level of catastrophe as the Challenger disaster" that destroyed a NASA space shuttle.
Scientists are not being blamed for this failure, even by the critics of the vaccine trials, such as, John P. Moore, an AIDS virologist at Weill Cornell Medical College. He states, "I do not think that what happened in this trial is an example of scientists blindly rushing into dangerous things. In the general HIV-research community, I didn't know anyone who said this was going to happen."
The problem is that scientists cannot seem to understand exactly what has gone wrong and cannot explain the results because the vaccine, developed by Merck, could not have caused HIV infection because it contains only three proteins from HIV, not the entire virus.
The trials were to determine if the vaccine was effective and the degree of effectiveness if it was, but nothing in the studies done on monkeys before they moved on to human trials, even hinted that the vaccine could be harmful at all.
There are theories and hypothesis, each one undercut by other factors and the scientists are left questioning what has happened and assessing whether anything gave hint that the results would be the opposite of what was expected.
The working hypothesis for what went wrong is that the vaccine somehow primed the immune system to be more susceptible to HIV infection -- a scenario neither foreseen nor suggested by previous studies.
At this point, no one is quite sure what effect this failure and setback means for the future of AIDS vaccines or any type of human trials.