New York Times Letter (1)

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Challenging a Theory
To the Editor:

The Doctor's World column "New Book Challenges Theories of AIDS Origin" on Nov. 30 describes the hypothesis that H.I.V., the virus that causes AIDS, was initially transmitted to humans during the first large-scale trials of oral polio vaccine in what was then the Belgian Congo. Although we are not named in the article, it is common knowledge in the scientific community that we conducted those trials. The hypothesis is based on the suggestion in a recently published book that we used chimpanzee cells to prepare the vaccine, and that these cells were, unknown to us, contaminated with a precursor of the human AIDS virus.

We wish to state categorically that no chimpanzee tissues were used by us for polio vaccine production.

Most scientists believe that H.I.V. originated from a chimpanzee virus, but there are other explanations for the transmission to humans that have nothing whatsoever to do with polio vaccination. The early cases of AIDS appeared where they would be expected to occur, in sites of relatively high population density.

Moreover, two independent analyses of the probable timing of the crossover of H.I.V. from chimpanzees into humans give dates far earlier than 1957-59, the years in which our polio vaccine was used in the Congo. We believe the book is likely to increase the concerns in Africa about the safety of polio vaccines, and indeed of other badly needed vaccines.

DR . STANLEY A. PLOTKIN Doylestown, Pa.  DR . HILARY KOPROWSKI Philadelphia

Dr. Plotkin is an emeritus professor of pediatrics at the University of Pennsylvania; Dr. Koprowski is a professor of microbiology and immunology at Thomas Jefferson University.