We would like to add two clarifications to your editorial and News story about the Royal Society meeting on the origin of human immunodeficiency virus (HIV) and the hypothesis that oral polio vaccine may have been contaminated1,2.
First, contrary to your statement, and as presented at the meeting, only two batches of vaccine were used in the mass vaccinations conducted in the Congo before 1959, the date of the first confirmed HIV infection in a human. No concrete or credible evidence exists that polio vaccine was produced locally in the Congo, and neither of the large lots produced in Philadelphia have been found to contain simian immunodeficiency virus (SIV) or HIV by the very sensitive polymerase chain reaction test conducted by independent laboratories3.
Second, you tax people in some other fields, particularly those working on xenotransplantation, with complacency about cross-species contamination. In the case of polio, we adapted attenuated vaccine strains to human diploid strains as soon as they became available, precisely because of concern regarding extraneous agents4.
Nature 407, 115 (2000).
Dickson, D. Nature 407, 117 (2000).
Plotkin, S. A. Phil. Trans. R. Soc. Lond. (in the press).
Hayflick, L., Plotkin, S. A., Norton, T. W. & Koprowski, H. Am. J. Hyg. 75, 240–258 (1962).