USIA Washington File - December 15, 1999
Washington -- AIDS researchers report that little scientific
evidence supports the recently publicized suggestion that the
origin of the human immunodeficiency virus (HIV) that causes
AIDS can be linked to an early oral polio vaccine tested on
about a million people in central Africa between 1957 and 1960.
The hypothesis, published in a recent book by British
journalist Edward Hooper, suggests that HIV-1 -- the virus
responsible for the global AIDS pandemic -- originated as a
result of the inadvertent inoculation of trial participants
with an HIV-like virus present in monkey kidney cell cultures
used to prepare the polio vaccine.
The suggestion first appeared in a 1992 Rolling Stone magazine
article that sought to link AIDS and the polio vaccine trials
A spokesman for the U.S. Centers for Disease Control and
Prevention in Atlanta, Georgia, said that the weight of
scientific evidence "does not support this idea, and there is
no more reason to believe this hypothesis than many others
which have been considered and rejected on scientific grounds."
The spokesman said that the same oral polio vaccine that was
used in central Africa was also tested on thousands of
individuals in Poland, but there was no evidence of early HIV
infection there. He added that since the 1960s, billions of
doses of oral polio vaccine have been delivered worldwide and
no association with HIV infection has ever been recorded.
Researchers report that most scientists have long believed that
the AIDS virus descended into humans from a primate species.
But up to now there had been scant data to support the thesis,
allowing theories such as the polio-virus vaccine hypothesis to
flourish. Last January, however, an international team of
scientists identified a subspecies of chimpanzees native to
west equatorial Africa as the original source of the AIDS
virus. The discovery was hailed as the best case yet for the
AIDS virus jumping from chimpanzees into humans.
The findings were announced at the opening of the largest
annual AIDS conference held in the United States and published
in the February 4 issue of Nature.
The research team, led by Dr. Beatrice Hahn of the University
of Alabama in Birmingham, found through careful molecular
analysis that a certain strain of chimpanzee virus is closely
related to human HIV-1 infections that cause AIDS. This virus
strain infects one particular chimp subspecies, called Pan
troglodytes troglodytes, found in a region that includes Gabon,
Cameroon and Equatorial Guinea.
Significantly, Dr. Hahn and her colleagues also found that the
natural habitat of these chimpanzees "coincides precisely" with
the regions in Africa that have had human HIV-1 infections for
the longest period of time. The scientists conclude that this
particular subspecies of chimpanzees is the natural reservoir
of HIV-1, and cite conclusive evidence that the virus has
spread from the chimpanzees to humans on three distinct
The researchers believe that HIV-1 was introduced into the
human population when hunters became exposed to infected
chimpanzee blood. Furthermore, they speculate that humans might
still be at risk from cross-species transmission because the
so-called bushmeat trade -- the hunting and killing of
chimpanzees and other endangered animals for human consumption
-- is still common practice in west equatorial Africa.
Dr. Anthony Fauci, director of the National Institute of
Allergy and Infectious Diseases, which helped fund the research
effort, said the findings had "significant potential."
"We now have chimpanzee isolates of simian immunodeficiency
virus (SIV) that have been shown to be closely related to
HIV-1," he said. "Furthermore, this virus infects a primate
species that is 98 percent related to humans. This may allow
us...to study infected chimpanzees in the wild to find out why
these animals don't get sick, information that may help us
better protect humans from developing AIDS."
Dr. John Moore, a lead researcher at the Aaron Diamond AIDS
Research Center in New York, said it is widely accepted that
humans became infected with HIV-1 through contact with
chimpanzees. He said the question is how did it get from chimps
"Certainly, the view that has the most credibility in the AIDS
research community is that it is a natural transmission event,"
he said. "When animals are captured and butchered for human
consumption -- and chimps are used as food in several parts of
Africa -- it is not too difficult to imagine that you would cut
yourself during the food preparation and virus transmission
would occur. No one can prove it happened, but it's certainly
the most immediately sensible idea."
Moore said, however, that Hooper's theory that a polio vaccine
produced in cultures of kidney cells from various primate
species could have been contaminated "by some strange set of
circumstances" with a virus that was later identified in humans
as HIV-1 "is extremely unlikely."
"It's not 100 percent impossible, but it's highly, highly
unlikely," Moore said. "He really has no evidence other than
speculation and coincidence to support his case."
Researchers also point out that different subspecies carry
different forms of the chimp virus and, if current research is
correct, the subspecies of chimp from central Africa whose
kidneys might have been used in the polio vaccine trials are
the "wrong" ones -- harboring only a distant relative to HIV-1.
The Wistar Institute, the private, non-profit organization that
produced the 1950s polio vaccine used in Africa, said it would
allow two independent laboratories to test material from the
vaccine trials in hopes that this will end the controversy by
showing no evidence of the chimpanzee form of the virus that
causes AIDS. Wistar said the labs are expected to receive the
material by the end of the year.
In 1995, Swedish scientists tested some of the vaccine used in
Africa and found no evidence of either the simian or human
immunodeficiency virus. However, the Swedes looked at only one
of two batches involved in the production of the vaccine, and
the new tests will encompass both. Experts report, however,
that negative results from the tests will not necessarily
resolve the controversy because other batches, either used up
or lost since the vaccine trials in Africa, might have been
Two Wistar scientists who led the polio research in Africa,
former institute director Hilary Koprowski and his former
deputy Stanley Plotkin, reject the suggestion that the vaccine
could have been the medium of transfer.
Koprowski said chimpanzees were used only to test the vaccine
and never to produce it. Instead, researchers made the vaccine
with kidney tissues from Asian rhesus macaque monkeys, whose
kidney cells do not support SIV or HIV.
"This book has only preconceptions. There are no facts," said
Koprowski, now professor of microbiology and immunology at
Thomas Jefferson University in Philadelphia.
"The idea is a house of cards built on circumstantial evidence,
and whatever doesn't fit has been ignored," said Plotkin, who
developed the modern rubella vaccine before leaving Wistar for
France's Pasteur Merrieux Connaught. "It's also, frankly, an
attack on people's reputations, and I feel it has to be dealt
The Wistar Institute faced similar assertions in 1992, when
Rolling Stone magazine published an article on the polio-AIDS
theory. At the time, the institute formed an outside panel of
scientists who concluded that the polio trials has not been
responsible for the spread of AIDS.
(The Washington File is a product of the Office of
International Information Programs, U.S. Department of State)