The overall expected rate of infection was not reduced in the high-risk people who volunteered for the study. However, the expected infection rate for the 314 black volunteers who received the vaccine was reduced by 78 percent — a finding the researchers said was unexpected. The rate was reduced by 67 percent for all nonwhite volunteers other than Hispanics.
AIDSVAX is formulated to protect against the “B” strain of the virus commonly seen in Europe and the United States. Researchers were not expecting AIDSVAX to be effective against strains circulating in Africa, the continent hardest hit by HIV.
VaxGen conducted the AIDSVAX trial in the United States, Canada, Puerto Rico and the Netherlands. It started in 1998 with 5,009 volunteers — mostly gay and bisexual men — who received seven injections over three years. Of those, 3,330 received the vaccine and 1,679 received placebo shots.
Although just 498 blacks and Asians were enrolled in the trial, the results are considered statistically significant. There is a less than a 2 percent chance that the results for blacks could have occurred by chance. The possibility that the results found in Asians occurred by chance is less than 1 percent.
“We’re not sure yet why certain groups have a better immune response,” VaxGen Vice President Phillip Berman said in a statement Sunday.
VaxGen’s results did show that black and Asian volunteers seemed to produce more antibodies against the virus than others. The company is working to determine whether a higher level of antibodies correlates with the prevention of infection.
VaxGen’s President Dr. Donald Francis said it was not immediately clear if its results would be enough to satisfy the U.S. Food and Drug Administration, which had been looking for at least a 30 percent rate of protection from infection. The FDA has never approved a vaccine based on its efficacy in a minority group.
The FDA had also been looking for some sign that the vaccine might reduce the ability of the virus to destroy a patient’s immune system. Francis said the company was still analyzing that data.
All participants in the study were counseled on how to prevent HIV infection. A study done by the Centers for Disease Control and Prevention indicated that everyone in the trial reduced risky behavior, such as having sex without a condom, VaxGen said. One fear had been that vaccinating people could make them overconfident and more likely engage in behavior that could cause infection.
Many vaccines use a live but weakened virus, or a “killed” virus, to stimulate the body’s immune response. But this is considered to be too dangerous to do with HIV, which integrates its genetic material into the human immune system cells it infects.
AIDSVAX uses two proteins, based on the gp-120 protein found on the outside of the virus. The hope was that the body’s immune system could become sensitized to anything carrying gp-120 and mount a response to the virus.
Other researchers had said that stimulating an antibody response using this approach would not be enough to vanquish HIV, which can mutate and evade the body’s immune responses.
“The scientific community involved in this field expected this vaccine trial to fail,” Dr. Norman Letvin, an AIDS vaccine researcher at Harvard Medical School, told Reuters.
“There are much more promising AIDS vaccines in the early phases of human testing right now and a failure of one strategy does not mean that these other strategies won’t be much more effective.”