There is conflicting evidence over whether some types of cancer might be linked to the contaminated vaccine.

Batches of polio vaccine tainted with "simian virus 40" (SV40) were given between 1955 and 1963. This was because monkey kidney cells were used in the jab's production process.

Traces of the monkey virus have been found in some human tumours, raising the possibility that it could play a role in the disease. However, this has not been supported by the majority of epidemiological data.

US cancer incidence data have not shown an increased incidence of pleural mesothelioma among the birth cohorts that were exposed to SV 40-contaminated poliovaccine US research team

The latest research, published in the Journal of the National Cancer Institute, looked at a rare cancer of the membrane that covers the lungs known as pleural mesothelioma.

There was a rise in cases of this cancer between the mid 1970s and the late 1990s, and the SV40 virus has been detected in some biopsy samples.

A US team looked at the incidence of the cancer in men and women of different age groups and compared it with trends in exposure to the tainted vaccine.

Howard Strickler and colleagues of the Albert Einstein College of Medicine in New York found no clear link.

Conflicting reports

The group most prone to pleural mesothelioma - men aged 75 or over - was least likely to have received the vaccine.

Furthermore, the cancer was rare in women even though they were just as likely to have been exposed to the contaminated poliovaccine as men.

Genetic traces of the virus have been found in tumours

Among those most heavily exposed to the early vaccine - men aged 25 to 54 - incidence rates of the cancer remained stable or decreased.

The authors say that after almost 40 years of follow-up, "US cancer incidence data have not shown an increased incidence of pleural mesothelioma among the birth cohorts that were exposed to SV40-contaminated poliovaccine".

They add, however, that continued surveillance of all people exposed to the vaccine is needed "in view of conflicting reports on the detection of SV40 genomic DNA sequences in mesothelioma tumour samples".

Aids controversy

The US study did not look at other types of cancer linked with the monkey virus such as non-Hodgkin's lymphoma, a cancer of the lymphatic system.

Previous research has found genetic "footprints" of the virus in 43% of the non-Hodgkin's tumour cells. There is no proof that SV40 causes the human cancer, although animal experiments suggest this can happen.

In addition, it is not proven that the polio vaccine was the source of the SV40.

Some patients born long after the contaminated batches were given have tested positive for the virus, yet scientists are unsure whether it is communicable between humans.

It has also been alleged that the virus which causes Aids was passed from primates to humans in contaminated batches of poliovaccine, although close examination of frozen samples of 1950s stock appear to suggest otherwise.