Sir

Your News and Opinion articles1,2 about alleged contamination of vaccines should serve as a warning against over-optimism.

These articles highlight the failure to show any evidence for contamination of Wistar Institute polio vaccine stocks by human and simian immunodeficiency viruses (HIV/SIV), and you appeal for a truce. But — although Edward Hooper is quoted as saying that “vaccine samples released did not include any from batches prepared for use in Africa” — lymphocytes have been detected in other polio vaccines3. Half of the vervet monkeys in Southern Africa are SIV positive; these animals were used for preparing early polio vaccines.

Considering the many millions of vaccine doses prepared in primary vervet monkey kidney cultures over a 30-year period, it is inconceivable that some SIV did not contaminate many cultures. By the same yardstick, simian virus 40 (SV40) contaminated millions of doses of poliovirus vaccine until the animals were screened for this tumour virus.

Edward Hooper and others surely do not intend to undermine the polio vaccine efforts. What is needed is a new awareness of the need for caution — remembering the example of BSE — in view of the current impetus towards xenotransplantation and the accompanying danger of contamination. Our aim should be to improve our vaccines, not to undermine public confidence in them.