Sarah Bennett
Between 1955 and 1963, an estimated 10-30% of polio vaccines administered in the US were contaminated with simian virus 40 (SV40). The virus was present in the tissue cultures from monkey kidneys used to grow poliovirus for the vaccines. SV40 is a monkey virus that can cause cancer in animals, and it has been found in some human tumors. While there is no conclusive evidence that SV40 causes cancer in humans, the possibility has raised concerns about the safety of the polio vaccine. The US government established testing requirements in 1961 to ensure that new polio vaccine batches were SV40-free, and no vaccines used today contain the virus. However, the question of whether SV40-contaminated polio vaccines caused cancer in humans remains a subject of ongoing research and public health attention.
| Characteristics | Values |
|---|---|
| Date of SV40 discovery | 1960 |
| Date SV40 contamination of polio vaccines occurred | 1955-1963 |
| Countries affected by SV40 contamination | United States and other countries |
| Number of people exposed to SV40 in the US | 98 million |
| Number of people exposed to SV40 in clinical trials | 10,000 |
| Type of polio vaccines contaminated | Inactivated polio vaccine (IPV) and oral polio vaccine (OPV) |
| Virus source | Monkey kidney cell cultures |
| Virus type | Simian vacuolating virus 40 (SV40) |
| Potential health risks | Cancer, neurological disorders |
| Status of SV40 in modern vaccines | Not present |
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What You'll Learn
- SV40 is a monkey virus that can cause cancer in animals
- SV40 was found in polio vaccines produced between 1955 and 1963
- The virus likely came from the monkey kidney cell cultures used to make the vaccines
- Studies suggest that SV40-contaminated polio vaccines did not increase the risk of cancer in humans
- The WHO recommended that all polio vaccines be SV40-free after 1961
SV40 is a monkey virus that can cause cancer in animals
SV40, or Simian Vacuolating Virus 40, is a monkey virus that has the potential to cause cancer in animals. It was first identified in 1960 when researchers found that between 10 and 30% of polio vaccines in the US were contaminated with SV40. The virus was present in the original seed strain or the substrate of primary kidney cells from infected monkeys, which were used to grow the vaccine virus.
SV40 is a polyomavirus, a type of DNA virus that can cause tumors in humans and animals. While it has not been conclusively established that SV40 causes cancer in humans, it has been linked to certain types of tumors, including brain and bone tumors, mesotheliomas, and lymphomas, as well as kidney diseases. Studies have shown that SV40 can induce sarcoma and ependymomas in hamsters inoculated with monkey cells infected with the virus.
The contamination of polio vaccines with SV40 occurred between 1955 and 1963, affecting millions of people worldwide. It is estimated that up to 30 million people in the United States alone may have been exposed to live SV40 during this period. The Institute of Medicine concluded that there was moderate strength evidence linking SV40 exposure from the polio vaccine to SV40 infection in humans.
While population-level studies have not shown extensive evidence of increased cancer incidence due to SV40 exposure, the virus has become a cause for concern among anti-vaccination activists. The hypothesis that SV40 might cause cancer in humans remains a controversial area of research, and further studies are needed to fully understand its potential impact on human health.
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SV40 was found in polio vaccines produced between 1955 and 1963
The polio vaccine administered between 1955 and 1963 was contaminated with a virus called simian virus 40 (SV40). The virus was found in both the oral polio vaccine (OPV) and the inactivated polio vaccine (IPV). The contamination came from the rhesus and cynomolgus macaque monkey kidney cell cultures used to produce the vaccine.
SV40 is a monkey virus that has the potential to cause cancer in animals, although it is considered unlikely to cause cancer in humans. After the discovery of SV40 in 1960, it was soon identified in early batches of the polio vaccine. The vaccines in which SV40 was found were produced between 1955 and 1961 by Lederle, now a subsidiary of Wyeth. The contamination may have been in the original seed strain or in the substrate—primary kidney cells from infected monkeys used during production.
In 1961, the U.S. government established requirements for testing to verify that all new lots of polio vaccine were free of SV40. However, potentially contaminated vaccine from previously approved lots of IPV was not recalled and may have been used until early 1963. From 1955 to 1963, an estimated 10-30% of polio vaccines administered in the US were contaminated with SV40.
Studies of groups of people who received the contaminated polio vaccine during this time provide evidence of no increased cancer risk. However, the Institute of Medicine's Immunization Safety Review Committee concluded that the evidence was inadequate to determine conclusively whether or not the contaminated polio vaccine caused cancer. Population-level studies also show no evidence of increased cancer incidence due to SV40 exposure.
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The virus likely came from the monkey kidney cell cultures used to make the vaccines
The polio vaccine was contaminated with Simian Virus 40 (SV40) between 1955 and 1963. The virus likely came from the primary kidney cells of infected monkeys, which were used to grow the poliovirus during vaccine production. The monkeys in question were rhesus and cynomolgus macaques, and the virus is known to infect these monkeys without causing symptoms.
SV40 was discovered in 1960 by Sweet and Hilleman, who found that it could infect the monkey kidney cells used to grow the poliovirus. The discovery of SV40 led to concerns about its potential impact on human health, particularly its ability to cause cancer in animals. Soon after its discovery, SV40 was also shown to be able to produce tumors in hamsters and transform human cells in culture. This raised serious concerns about the potential impact of the contaminated polio vaccine on humans.
The contamination was found in both the oral polio vaccine (OPV) and the inactivated polio vaccine (IPV). The OPV was produced using live virus, while the IPV used a formaldehyde inactivation technique that did not reliably kill SV40. As a result, most of the SV40 contamination was found in the IPV. Once the contamination was recognized, steps were taken to eliminate it from future vaccines, and the U.S. government established testing requirements to verify that all new lots of polio vaccines were free of SV40.
The potential impact of the SV40-contaminated polio vaccine on human health has been a subject of ongoing research and controversy. While SV40 has biological properties consistent with a cancer-causing virus, it has not been conclusively established that it causes cancer in humans. Studies of groups who received the contaminated vaccine have not shown an increased risk of cancer. However, the Institute of Medicine's Immunization Safety Review Committee has concluded that the evidence is inadequate to determine whether or not the contaminated vaccine caused cancer due to flaws in the epidemiological studies.
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Studies suggest that SV40-contaminated polio vaccines did not increase the risk of cancer in humans
The contamination of polio vaccines with Simian Virus 40 (SV40) occurred in the United States and other countries between 1955 and 1963. SV40 is a monkey virus that has the potential to cause cancer in animals, but it is considered unlikely to cause cancer in humans. The virus was present in the monkey kidney cell cultures used to produce the vaccine, and while it was found in both the oral and injectable forms of the polio vaccine, most of the contamination was in the inactivated polio vaccine (IPV).
Studies of groups of people who received the polio vaccine during the period of contamination provide evidence that there was no increased cancer risk associated with the contaminated vaccine. However, these epidemiologic studies have been criticized as flawed, and the Institute of Medicine's Immunization Safety Review Committee concluded that the evidence was inadequate to determine conclusively whether or not the contaminated polio vaccine caused cancer in humans.
The committee's review of the epidemiologic and biological evidence showed that the effects of exposure to the contaminated polio vaccine remain uncertain, and more research is needed to fully understand the role of SV40 in human cancers. While SV40 has biological properties consistent with a cancer-causing virus, and has been found in certain human tumors, the etiologic role of the virus in tumorigenesis has not been established.
Some researchers have found SV40 in human ependymomas, choroid plexus tumors, bone tumors, and mesotheliomas, but SV40-like DNA sequences were not detectable in Finnish mesothelioma patients who had not been exposed to SV40-contaminated polio vaccines. This suggests that the contaminated vaccine may not have been a significant factor in the development of these cancers.
In summary, while SV40-contaminated polio vaccines may have had the potential to cause cancer in humans, the available evidence does not indicate an increased risk of cancer in those who received the contaminated vaccine. More research is needed to definitively resolve the question of whether SV40 contamination caused cancer in humans.
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The WHO recommended that all polio vaccines be SV40-free after 1961
The World Health Organization (WHO) recommended that all polio vaccines be SV40-free after 1961. This was prompted by the detection of SV40 in some human tumors. SV40, or Simian Virus 40, is a monkey virus that has the potential to cause cancer in animals, although it is considered unlikely to affect humans. The virus was discovered in 1960 in the rhesus monkey kidney cells used to prepare the poliovirus vaccines. It was also found to be present in stocks of the injected form of the IPV (inactivated poliovirus vaccine) in use between 1955 and 1963, and some polio vaccines prepared from 1954 to 1961 were contaminated with infectious SV40.
The contamination may have occurred in the original seed strain or the substrate, which included primary kidney cells from infected monkeys. The manufacturers of the polio vaccines had to address two main problems to eliminate SV40 from their vaccines. Firstly, around 50% of rhesus monkeys were endemically infected with SV40, and the infection could easily spread to uninfected caged monkeys. Secondly, during production, the harvest from the kidneys of different monkeys was often pooled, meaning that even one SV40-infected monkey could contaminate an entire batch of the vaccine. To solve this issue, manufacturers switched to using African green monkeys as they are SV40-free.
Despite the contamination, studies of groups of people who received the polio vaccine during 1955-1963 provide evidence of no increased cancer risk. A large study in Sweden also examined cancer rates of 700,000 individuals who had received potentially contaminated polio vaccines and revealed no increased cancer incidence. However, the question of whether SV40 causes cancer in humans remains controversial, and improved assays for the detection of SV40 in human tissues are needed.
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Frequently asked questions
No, SV40 is no longer present in the polio vaccine. It is believed that all polio vaccines were SV40-free in the US after 1961 and in other countries after 1962.
SV40 stands for Simian Virus 40, a monkey virus that has the potential to cause cancer in animals. It was discovered in the 1950s when it was found to contaminate the polio vaccine.
While SV40 has biological properties consistent with a cancer-causing virus, it has not been conclusively established that it causes cancer in humans. Studies have found no increased cancer risk in people who received the contaminated polio vaccine from 1955-1963. However, the Institute of Medicine's Immunization Safety Review Committee recommends continued research to resolve this question.
