THAILAND—An AIDS vaccine tested on more than 16,000 male and female volunteers surprised researchers when it demonstrated the first-ever small, but measurable, ability to reduce a person’s risk of becoming infected with the disease. The Surgeon General of the U.S. Army, the six-year trial’s sponsor, announced Thursday the prime-boost investigational vaccine regimen was safe and 31 percent effective in preventing HIV infection.
The complicated series of “prime” and “booster” inoculations engendered excitement among researchers who have sought a miracle drug for 20 years.
“These new findings represent an important step forward in HIV vaccine research,” Anthony S. Fauci, M.D., director of the National Institute of Allergy and Infectious Diseases, said in a statement released Thursday. The NIAID, a department of the National Institutes of Health, provided the majority of funding for the $105-million study at an undisclosed clinic in Thailand. “For the first time, an investigational HIV vaccine has demonstrated some ability to prevent HIV infection among vaccinated individuals. Additional research is needed to better understand how this vaccine regimen reduced the risk of HIV infection, but certainly this is an encouraging advance for the HIV vaccine field.”
“Conceptually, we now know a vaccine is possible,” he told The Washington Post. “Whether the vaccine is going to look anything like this one, I don’t know. But at least we know it can be done.”
According to physicians involved in the study, the most likely use of the data will be in providing specific information about how the human immune system responds to the AIDS virus when a subject is even moderately protected from the disease. The NIAID said the vaccine regimen had no effect on the amount of virus in the blood of volunteers who acquired HIV infection during the study, whether those volunteers received the investigational vaccine or a placebo.
Though the study’s results were promising, skeptics were quick to point out what they consider aspects that will keep the results from being globalized. For one thing, the vaccine combos were targeted to strains of HIV common in Southeast Asia. Each geographic area of the world is subject to slightly different strains of the virus. For another, the study included few intravenous drug users or homosexual men—two groups at greatest risk of HIV infection in North America and Europe. In Africa and Asia, heterosexual intercourse is the most common transmission vector.
About 40 percent of the volunteers were women, and all subjects were between the ages of 18 and 30, young and otherwise healthy. All were counseled about how to prevent the spread of HIV/AIDS.
Of the 8,198 research subjects who received placebo injections during the study, 74 contracted HIV in the three years following their vaccination regimen. In contrast, 51 of 8,197 participants who received the investigational vaccine became infected. The level of effectiveness in preventing HIV infection is considered statistically significant, yet researchers could not dismiss the role chance may have played in the results.
The regimen was composed of two vaccines: ALVAC-HIV vaccine (the primer dose), a modified canarypox vaccine developed by Sanofi Pasteur, based in Lyon, France; and AIDSVAX B/E vaccine (the booster dose), a glycoprotein 120 vaccine developed by Vaxgen Inc. and now licensed to San Francisco-based Global Solutions for Infectious Diseases (GSID). The vaccines are based on the subtype B and E HIV strains that commonly circulate in Thailand. The subtype B HIV strain is the one most commonly found in the U.S.
Interestingly, previous studies of the two vaccines showed neither AIDSVAX nor ALVAC—which were designed to stimulate different immune responses in the presence of HIV infection—offered protection on its own. How the two work together to prevent infection is one of the mysteries scientists intend to investigate in future studies.
“The Thai study demonstrates why the HIV vaccine field must take a balanced approach to conducting both the basic research needed to discover and design new HIV vaccines and, when appropriate, testing candidate vaccines in people,” Margaret I. Johnston, Ph.D., director of NIAID’s Vaccine Research Program within the Division of AIDS, said in Thursday’s prepared statement. “Both avenues provide critical information that will continue to help us better understand what is needed to develop a fully protective HIV vaccine.”
