SV40 was found to be present in stocks of the injected form of the polio vaccine (IPV) in use between 1955 to 1963.[53] It is not found in the OPV form.[53] Over 98 million Americans received one or more doses of polio vaccine between 1955 to 1963 when a proportion of vaccine was contaminated with SV40; it has been estimated that 10–30 million Americans may have received a dose of vaccine contaminated with SV40.[53]Later analysis suggested that vaccines produced by the former Soviet bloc countries until 1980, and used in the USSR, China, Japan, and several African countries, may have been contaminated; meaning hundreds of millions more may have been exposed to SV40.[58]
SV40 virus has been found in certain types of cancer in humans, but it has not been determined that SV40 causes these cancers.
The EEVM samples that we tested were produced in 1966 and 1969; therefore, we show that SV40 contaminated some polio vaccines at least until that period. The EEVM vaccine samples we tested ( Table 1) were produced with the same seed virus that was used until 1978, apparently without any further purification to remove SV40. Therefore, it is possible that the EEVM vaccines may have remained SV40 contaminated until 1978 when a new seed was produced. We have no information about this seed virus or vaccines produced from it. Therefore, based on our data, we could not determine the exact time when EEVM vaccines became SV40 free but can suggest that it may have happened in the 1980s when EEVM switched to seed virus stocks provided by the WHO that we found to be free of SV40.