AIDSVAX, an experimental HIV vaccine being developed by VaxGen Inc., does not appear to provide significant protection against HIV infection, company officials announced Monday. VaxGen released data from a Phase III clinical trial that showed the vaccine did not appear to protect most whites and Latinos from infection, though it did show some promise in reducing HIV infections among blacks and Asians. Of the 314 black clinical trial participants, the expected infection rate was 78% lower among those taking the vaccine compared with those who received a placebo. Among Asians, the expected rate was cut by 67%. The overall reduction of expected infection rate among all 5,417 study volunteers was only 3.8% compared with a control group that received a placebo.
"This is the first time we have specific numbers to suggest that a vaccine has prevented HIV infection in humans," VaxGen vice president Phillip Berman said. "We're not sure yet why certain groups have a better immune response."
AIDSVAX is the first HIV vaccine to make it to human trials. The vaccine aims to produce an antibody response to invading HIV by using the gp120 protein from the outer shell of the virus to prime the immune system into recognizing and attacking the virus in the body. The Phase III clinical trial consisted of 5,108 gay or bisexual men and 309 women who were at high risk for HIV infection because they had sex partners who injected drugs or had sex with men. Overall, 5.7% of participants who received the vaccine became infected with HIV during the three years of the trial, compared with 5.8% of the people who received the placebo.
All of the study participants were HIV-negative at the beginning of the three-year trial and received counseling on how to prevent HIV infection. They also were told not to rely on the vaccine to protect them against the virus. The vaccination schedule included three shots each month for the first three months of the study, followed by booster shots every six months.
Vaccines for any disease are usually required to be a minimum of 70% effective in preventing new infections in order to receive approval for widespread use. However, the Food and Drug Administration announced late last year that it would consider approving an HIV vaccine that proved at least 30% effective in the general population. VaxGen officials plan to continue developing and studying AIDSVAX for possible use in black and Asian communities. The company also is expected to announce the results of another clinical trial of the vaccine this fall that included 2,400 injection-drug users in Thailand.
AIDS activists and researchers were mixed in their reaction to VaxGen's announcement. Jose Esparza, director of AIDS vaccine research for the Joint United Nations Programme on HIV/AIDS, told USA Today that the trial results are "probably the most important accomplishment in vaccine research in 15 years," adding, "This is the first time anyone has shown protection [against HIV] in humans. The results tell us that a vaccine can protect humans against HIV."
Seth Berkley, president and CEO of the International AIDS Vaccine Initiative, told BBC News that the findings are "disappointing" but added, "We are not discouraged. The search for an AIDS vaccine will and must go on. Alternative AIDS vaccines, employing different design strategies, are now in development, and some have already entered human trials. These must move forward through further study without delay."