§ Mr. Gordon Marsden
To ask the Secretary of State for Health, pursuant to his answer of 21 July 1999,Official Report, column 548, what assessment he has made of the implications of contamination of polio vaccine in the United Kingdom with simian virus 40 between 1955 and 1963, for the development of cancers in humans. 
§ Yvette Cooper
SV40 (simian vacuolating virus 40) is a virus found in some species of monkeys. The polio virus in inactivated polio vaccine (IPV) used in the 1950s and early 1960s was grown on monkey kidneys, some of which have been shown to be potentially contaminated with SV40 virus. Concern about the possible impact of SV40 on the human population was raised in the early 1960s and precautions to prevent contamination were introduced internationally in 1962, shortly after the virus was identified. SV40 has been shown to be oncogenic in certain animals and has been found in several human tumours. It is not known whether SV40 causes the human tumours or whether it is just coincidentally present in the tumours. However, research studies in people who received potentially SV40 contaminated IPV have found no increase in cancers when compared with people who did not receive potentially contaminated IPV.
The National Institute of Biological Standards and Control (NIBSC) has tested stored polio vaccine using the most sensitive available modern molecular biological techniques to check whether the precautions introduced in the 1960s were effective. All the polio vaccines used since 1980 have been shown to be free of SV40 and all vaccines used since 1962 for which samples could be located are also free. Samples of IPV from the 1950s to the 1960s were not available. Serological studies have been conducted with the Public Health Laboratory Service which showed no evidence of increased antibody to SV40 in people receiving polio vaccine. In all ages of the people tested, about 5 per cent. had SV40 virus antibodies, suggesting that the virus may have been present in humans for a very long time and hence these antibodies are unlikely to have come from SV40 contaminated polio vaccine.
This issue has been considered by the Joint Committee on Vaccination and Immunisation, the Government's independent expert advisory committee, which has expressed reassurance as a result of the NIBSC work. NIBSC' s study has been published (Biologicals (1999), vol. 27, pps 1–10) copies of which are available in the Library.