SV40 - Polio Vaccine Contamination

Polio Vaccine Contamination

Soon after its discovery, SV40 was identified in the injected form of the polio vaccine produced between 1955 and 1961. This is believed to be due to kidney cells from infected monkeys having been used to grow the vaccine virus during production. 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, by means of formaldehyde, did not reliably kill SV40.

It was difficult to detect small quantities of virus until the advent of PCR; since then, stored samples of vaccine made after 1962 have tested negative for SV40, but no samples prior to 1962 could initially be found. Then, in 1997, Herbert Ratner of Oak Park, Illinois, gave some vials of 1955 Salk vaccine to researcher Michele Carbone. Dr. Ratner, the Health Commissioner of Oak Park at the time the Salk vaccine was introduced, had kept these vials of vaccine in a refrigerator for over forty years., Upon testing this vaccine, Dr. Carbone discovered that it contained not only the SV40 strain already known to have been in the Salk vaccine (containing two 72-bp enhancers) but also the same slow-growing SV40 strain currently being found in some malignant tumors and lymphomas (containing one 72-bp enhancers). It is 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. Although horizontal transmission between people has been proposed, it is not clear if this actually happens and if it does, how frequently it occurs.

An analysis presented at the Vaccine Cell Substrate Conference in 2004 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 unknowingly.