Definition of polio vaccine contamination

1) There is strong suspicion that polio vaccines produced between 1955 and 1962 were contaminated with SV40, because the kidney cells the vaccine virus was grown in came from infected monkeys. Both the Sabin vaccine (oral, live virus) and the Salk vaccine (injectable, killed virus) were affected; the technique used to inactivate the polio virus in the Salk vaccine did not reliably kill SV40.

It was difficult to detect small quantities of virus until the advent of PCR testing; since then, stored samples of vaccine made after 1962 have tested negative for SV40, but no samples prior to 1962 could be found. Thus, although over 10 million people received the potentially contaminated batches of vaccine, there is no way to know whether they were exposed to the virus, and if so, whether it was in a quantity and by a route that would cause infection. It is also unknown how widespread the virus was among humans before the 1950s, though one study found that 12% of a sample of German medical students in 1952 had SV40 antibodies. It is not known whether the virus can be transmitted between humans.

An analysis presented at the Vaccine Cell Substrate Conference in 2004 [1] ( suggested that vaccines used in the former Soviet bloc countries, China, Japan, and Africa, could have been contaminated up to 1980, meaning that hundreds of millions more could have been exposed to the virus.