HIV Vaccine Volunteer Update

National Institute of Allergy and infectious Diseases
National Institutes of Health
May 1997
HIV Vaccine Volunteer Update
The National Institute of Allergy and Infectious Diseases (NIAID) supports studies of
experimental vaccines intended to prevent infection and disease caused by the human
immunodeficiency virus (HIV). Since 1988, more than 2,100 healthy, non-HIV-infected adult
volunteers have enrolled in 27 NIAID-supported trials involving 17 vaccines. Approximately 80
percent of these individuals have received vaccines, and the remainder (20 percent) have received
placebos. The trials have been conducted at university-based AIDS Vaccine Evaluation Group
(AVEG) sites throughout the United States. NIAID investigators have carried out an additional
trial involving 120 volunteers at the National Institutes of Health Clinical Center in Bethesda,
Md., and currently are enrolling volunteers in a new trial of a DNA vaccine.
The trials conducted to date have tested the safety and the effects on the immune system
of several candidate vaccines made by genetic engineering techniques or by chemical synthesis.
Because the vaccines do not contain infectious or altered virus, volunteers cannot become
infected with HIV from the vaccines.
Participants have tolerated the vaccines well, and investigators have identified no pattern
of unexpected or significant adverse events related to immunization. To date, 26 participants
have become infected with HIV in the course of the AVEG studies. Of the 26, four were among
those who received placebo and 22 were among those who received vaccines. In addition, three
participants who received vaccines in NIAID's intramural trial became infected. The proportion
of volunteers who have become infected is similar in both the placebo and vaccination groups.
While it is clear that these vaccines are less than 100 percent effective in preventing HIV
infection, no further conclusions regarding their effectiveness can be drawn. Some participants
became infected before a full course of planned immunizations. In addition, because the size of
the trials and numbers of infections are too small, the overall efficacy of the vaccines in
preventing either infection or disease cannot be evaluated.
Investigators expect that some individuals in HIV vaccine trials will become infected
despite careful counselling about ways to reduce their risk of HIV infection. All infections
among the trial participants are the result of high-risk behaviors such as unprotected sex with an
HIV-infected individual or injection drug use. At present, none of the HIV-infected participants
has symptoms of AIDS, although two vaccinated individuals who became infected with HIV
experienced a rapid loss of CD4+ T cells. Investigators do not know whether this rapid CD4+ Tcell decline is related to vaccination. Similar rates of CD4+ T-cell loss have occurred in some
HIV-infected people who had not participated in vaccine trials.

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