[Letter to Jack Chow from Anthony Fauci]

DEPARTMENT OF HEALTH & HUMAN SERVICES Puci: -ea 2 eNational Institutes of Health
National Institute of Allergy
and Infectious Diseases
Bethesda, Maryland 20892
June 7, 1991
Dr. Jack Chow
White House Science Office
494 Old Executive Office Building
17th and Pennsylvania Avenue
Washington, D.C. 20506
Dear Dr. ow
In response to your request to the Division of AIDS, NIAID, we are pleased to
forward the enclosed information on the testing of AIDS/HIV vaccines by the
NIAID AIDS Vaccine Clinical Trials Network. I would like to-take this
opportunity to provide you with some additional information about the testing
of candidate vaccines for'AIDS, particularly phase II/III clinical trials.
The issue of phase II/III AIDS vaccine clinical trials is very complex, and
one that has been considered by various groups of experts over the past year,
most recently on April 29 by the National Institutes of Health (NIH) AIDS
Program Advisory Committee.
Two very important considerations impact the conduct of phase II/III vaccimtrials: 1) the conduct of these trials in humans is extremely costly; and
2) these trials would require the participation of a large number of
uninfected individuals who are at high risk for exposure to HIV. Because,C
cost considerations and the recognition that the defined populations in wLi,
to test vaccines are limited, we would thus want to test only those vacci-2
candidates that show the most promise of inducing protective immunity. T,
determination of what criteria to use to identify such promising candidate;
before moving ahead into phase II/III efficacy studies in humans has been 3
key focus of much of the recent discussion.
A question that is being asked today is whether scientific consensus exists
about the likely safety and efficacy of a particular approach to an AIDS
vaccine. There are two distinct issues regarding the approach to an AIDS
vaccine: 1) the question of whether a vaccine's success should be shown ''
in animal models before beginning large efficacy trials; and 2) the select.
of vaccine type.
On the first issue, there is considerable agreement among the top scientist
in the field that a vaccine should first show safety and the ability to
prevent infection (or possibly disease) in animals before large efficacy
trials in people should be initiated. This consensus is based on several
attributes of HIV and our level of understanding of it: 1) the lack of
knowledge of what confers immunity to HIV; 2) our limited understanding a-.
the degree of individual variation in the immune response and the complex'
of immune response to the virus; 3) the high degree of viral genetic varia*

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