A new report by the Institute of Medicine’s Immunisation Safety Review Committee has reviewed studies into the carcinogenic potential of SV40-contaminated polio vaccine.

A draft of the IOM report, entitled ‘Immunisation Safety Review: SV40 Contamination of Polio Vaccine and Cancer’, has concluded that, while it is clear that SV40 can cause cancer in animals, 'It has not been conclusively established' that the virus causes cancer in human beings. The IOM, however, admits that most of the studies were flawed and, based on this evidence, cannot rule out the possibility that the vaccine may have increased cancer risk in humans (Lancet, 2002; 360: 1307).

The report comes on the heels of a study indicating that the vaccine may be tied to the development of non-Hodgkin’s lymphoma. The researchers looked at hundreds of tumours taken from various cancer patients, and compared them with 68 samples taken from non-Hodgkin’s patients. They found genetic 'footprints' of the virus in 43 per cent of the non-Hodgkin’s tumour cells. In other types of tumour, some had no trace of the virus at all, and fewer than 10 per cent of most other types tested positive. Tissue taken from 40 apparently healthy patients produced no positive tests at all.

In the same issue, the Lancet also printed the results of a separate experiment, carried out at the Baylor College of Medicine in Houston, which tested more than 150 non-Hodgkin’s tumours and found virtually identical results - 42 per cent of the tumours had the SV40 ‘footprint’, while 186 non-malignant control samples all tested negative (Lancet, 2002; 359: 817-23).