Early polio vaccine harbored virus now feared to cause cancer in humans
San Francisco Chronicle
Rogue virus in the vaccine
Early polio vaccine harbored virus now feared to cause cancer in humans
William Carlsen, Chronicle Staff Writer
A growing number of medical researchers fear that a monkey virus that
contaminated polio vaccine given to tens of millions of Americans in the
1950s and '60s may be causing rare human cancers.
For four decades, government officials have insisted that there is no
evidence the simian virus called SV40 is harmful to humans. But in recent
years, dozens of scientific studies have found the virus in a steadily
increasing number of rare brain, bone and lung-related tumors - the same
malignant cancer SV40 causes in lab animals.
Even more troubling, the virus has been detected in tumors removed from
people never inoculated with the contaminated vaccine, leading some to
worry that those infected by the vaccine might be spreading SV40.
The discovery of SV40 in human tumors has generated intense debate within
the scientific community, pitting a handful of government health officials,
who believe that the virus is harmless, against researchers from Boston to
China who now suspect SV40 may be a human carcinogen. At stake are millions
of research dollars and potential medical treatments for those afflicted
with the cancers SV40 may be causing.
In April, more than 60 scientists met in Chicago to discuss the
controversial virus and how it works to defeat certain cells' natural
defenses against cancer.
"I believe that SV40 is carcinogenic (in humans)," said Dr. Michele Carbone
of Loyola University Medical Center in Maywood, Ill. "We need to be
creating therapies for people who have these cancers, and now we may be
able to because we have a target - SV40."
But scientists at the National Cancer Institute say their studies show
almost no SV40 in human tumors and no cancer increase in people who
received the contaminated vaccine.
"No one would dispute there's been a widespread, very scary exposure to the
population of potentially cancer-causing virus," said Dr. Howard Strickler,
NCI's chief investigator. "But none of our studies and other major analyses
have shown an inkling of an effect on the population."
Critics charge, however, that the few studies done by the government are
scientifically flawed and that health officials have downplayed the
potential risks posed by SV40 ever since they learned in 1961 that the
virus contaminated the polio vaccine and caused tumors in rodents.
"How long can the government ignore this?" asked Dr. Adi Gazdar, a
University of Texas Southwestern Medical Center cancer researcher. "The
government has not sponsored any real research. Here's something possibly
affecting millions of Americans, and they're indifferent.
"Maybe they don't want to find out."
The recent SV40 discoveries come at a time of growing concern over the
dangers posed by a range of animal viruses that have crossed the species
barrier to humans, including HIV, which scientists now believe came from
chimpanzees and ultimately caused the AIDS epidemic.
Based on dozens of interviews and a review of the medical research, this is
the story of how the campaign to eradicate polio may have inadvertently
permitted another potentially deadly monkey virus to infect millions of
people - and why the government for years discounted the accumulating
evidence suggesting that SV40 may be a health risk for humans.
Polio epidemic, 1955
During the first half of the 20th century, polio struck down hundreds of
thousands of people, leaving many paralyzed - some in iron lung machines -
and killing others. The worst year was 1952, when more than 57,000 polio
cases were reported in the United States. Three thousand died.
Then on April 12, 1955, Dr. Jonas Salk, a slightly built, soft-spoken
researcher from Pittsburgh, mounted the podium at the University of
Michigan and announced that he had developed a vaccine. That afternoon, the
government licensed the vaccine for distribution.
Salk's vaccine was made by growing live polio virus on kidney tissue from
Asian rhesus monkeys. The virus was then killed with formaldehyde. When the
vaccine was injected in humans, the dead virus generated antibodies capable
of fending off live polio.
Dr. Dwight Murray, then chairman of the American Medical Association,
called Salk's announcement "one of the greatest events in the history of
Within weeks, the stockpiled vaccine was being injected into the arms of
millions of people worldwide.
Virus and the tumors, 1959
Four years later, Bernice Eddy, a researcher at the National Institutes of
Health, noticed something strange while looking through her microscope.
Monkey kidney cells - the same kind used to make the vaccine - were dying
without apparent cause.
So she tried an experiment. She prepared kidney extracts from eight to 10
rhesus monkeys and injected tiny amounts under the skin of 23 newborn
hamsters. Within nine months, "large, malignant, subcutaneous tumors"
appeared on 20 of the animals.
On July 6, 1960, concerned that a monkey virus might be contaminating the
polio vaccine, Eddy took her findings to Dr. Joseph Smadel, chief of the
NIH's biologics division. Smadel dismissed the tumors as harmless "lumps."
The same year, however, at a Merck laboratory in Pennsylvania, Dr. Maurice
Hilleman and Dr. Ben Sweet isolated the virus. They called it simian virus
40, or SV40, because it was the 40th virus found in rhesus kidney tissue.
Immunization campaign, 1961
By then, the nation was winning the war against polio. Nearly 98 million
Americans - more than 60 percent of the population - had received at least
one injection of the Salk vaccine, and the number of cases was plummeting.
At the same time, an oral polio vaccine developed by virologist Albert
Sabin was in final trials in Russia and Eastern Europe, where tens of
millions had been inoculated, and it was about to be licensed in the United
States. Unlike the Salk vaccine, the oral version contained a live but
weakened form of polio virus and promised lifelong immunity.
But U.S. Public Health Service officials were worried. Tests had found SV40
in both the Sabin and Salk vaccines - it was later estimated that as much
as a third of the Salk vaccine was tainted - and that SV40 was causing
cancer in lab animals.
In early 1961, they quietly met with the agency's top vaccine advisers. The
agency found no evidence that the virus had been harmful to humans, but in
March, the officials ordered manufacturers to eliminate SV40 from all
New procedures were adopted to neutralize the tainted polio virus seed
stock and SV40-free African green monkeys were used to produce the bulk
vaccine instead of rhesus monkeys.
But officials did not recall contaminated Salk vaccine - more than a year's
supply - still in the hands of the nation's doctors.
And they did not notify the public of the contamination and SV40's
carcinogenic effect on newborn hamsters.
Hilleman would later explain that government officials were worried that
any potentially negative information could ignite a panic and jeopardize
the vaccination campaign.
The first public disclosure that the Salk vaccine was contaminated came in
the New York Times on July 26, 1961. A story on Page 33 reported that Merck
and other manufacturers had halted production until they could get a
"monkey virus" out of the vaccine.
When asked to comment, the U.S. Public Health Service stressed there was no
evidence the virus was dangerous.
No cause for alarm, 1962
The next year, a young Harvard-trained epidemiologist named Dr. Joseph
Fraumeni joined the National Cancer Institute and was assigned one of the
agency's most important projects: to determine if there was any cancer
increase among those injected with the Salk vaccine.
His research would form the basis of the government's position for decades.
Working with two colleagues, Fraumeni tested stored vaccine samples from
May and June of 1955, the first months of the national immunization
campaign, then ranked the samples according to how much SV40 they contained
- no, low or high amounts.
It would be the only time U.S. health officials measured the level of SV40
in the 1955-1962 vaccine. Stored samples from that period were later
Fraumeni identified the states where the SV40-contaminated vaccines had
been distributed during those two months. California, for example, received
vaccine with a low level of the virus.
The study looked at cancer mortality rates for 6- to 8-year-old children
vaccinated during that narrow time frame, tracking the group for four years.
The findings, which were published in the Journal of the American Medical
Association, showed no significant difference in cancer deaths in states
with high or low levels of SV40 in the vaccine when compared with cancer
deaths in states with no SV40 in the vaccine.
Cleveland children, 1976
Fourteen years later, after isolated reports linking the virus and human
cancers, Fraumeni decided to look at another group that had received
The group had been the subject of experiments conducted in the early 1960s
at Cleveland Metropolitan General Hospital. To determine the effect of
different amounts of the vaccines, researchers at the hospital inoculated
newborns from mostly lower-income black families with doses ranging up to
more than 100 times the dose recommended for adults.
The experiments took place over three years and involved 1,073 infants.
Most were given Sabin oral vaccine later determined to contain SV40.
From 1976 to 1979, Fraumeni and his associates sent letters to the
children - now age 17 to 19 - but fewer than half responded. The
researchers found no SV40-related health problems from exposure to
However, their 1982 report published in the New England Journal of Medicine
acknowledged the study's limitations: A majority of the children had not
responded; SV40-related cancers might take longer than 17 to 19 years to
develop, and SV40 appears less likely to infect humans through the oral
Nevertheless, they called their findings "reassuring and consistent with
the prevailing view that SV40 is not carcinogenic in human beings."
Then they decided to end the study, citing "the mounting complexities and
obstacles in tracing this particular group and the negative results to date."
The study's closure appeared to end the government's research into the
virus. But a few years later there would be a tectonic shift in SV40 research.
First discovery, 1988
In Boston, two researchers stumbled onto something disturbing.
Dr. Robert Garcea and his assistant, Dr. John Bergsagel, were using a
powerful new tool called polymerase chain reaction, or PCR, to look for a
pair of common human viruses in children's brain tumors.
But a different DNA footprint kept popping up in more than half the tumors.
They finally realized they were seeing SV40.
For more than a decade, scientists had reported sporadic findings of SV40-
like proteins in human tumors. But the earlier tests were primitive and the
results suspect. PCR, however, is capable of amplifying infinitesimal
fragments of DNA, which makes detections far more credible.
The findings were troubling. The researchers noted in their published
report that the children were too young to have received the contaminated
vaccine. But somehow the virus had infected them and embedded itself in
That same year, Dr. Michele Carbone was surprised to find a milky, rindlike
tumor in a laboratory hamster at the National Institutes of Health in
The animal was one of a group given an SV40 injection directly into their
hearts. Sixty percent of those hamsters developed the fatal cancer called
Carbone, a postdoctoral fellow at the institute, knew that SV40 caused
tumors in hamsters but only in specific locations where large doses of
virus were injected. Here the mesothelial membrane lining the lungs
apparently became cancerous from minuscule amounts of SV40 shed by the tip
of the needle on the way to the hamsters' hearts.
So he tried another experiment, this time injecting SV40 directly into the
thin mesothelial walls of another group of hamsters. Within six months,
every animal developed mesothelioma.
Carbone was puzzled. Mesothelioma is a rare cancer. Few human cases were
reported before the 1950s, but its incidence had been increasing steadily,
reaching several thousand cases a year in the United States by 1988.
Studies had linked mesothelioma to asbestos exposure - with tumors usually
appearing many decades later. Yet 20 percent of victims had no asbestos
Carbone decided to use PCR to test 48 human mesotheliomas stored at the NIH.
He was stunned: 28 of them contained SV40.
More cancers, 1996
PCR unleashed a wave of SV40 discoveries.
By the end of 1996, dozens of scientists reported finding SV40 in a variety
of bone cancers and a wide range of brain cancers, which had risen 30
percent over the previous 20 years.
Then, Italian researchers reported finding SV40 in 45 percent of the
seminal fluid samples and 23 percent of the blood samples they had taken
from healthy donors.
That meant SV40 could have been spreading through sexual activity, from
mother to child, or by other means, which could explain how those never
inoculated with the contaminated vaccine, such as the Boston children, were
Government assurances, 1996
At the National Cancer Institute in Bethesda, officials were growing
increasingly concerned about the SV40 discoveries.
The findings were of particular interest to Fraumeni, who had been promoted
to director of NCI's Division on Cancer Epidemiology and Genetics. His
earlier studies concluding that SV40 posed little or no health risk were
now under challenge.
But the scientific community was skeptical of the recent SV40 discoveries.
As a potent carcinogen in lab animals, SV40 had been used for years as a
tool to study cancer. Therefore, the powerful PCR test was suspected of
finding stray SV40 fragments that might have contaminated laboratories.
So Dr. Howard Strickler, one of Fraumeni's epidemiologists, led a study
using PCR on 50 mesotheliomas from Armed Forces hospitals across the
country. And he found no SV40.
Although the findings bolstered the government's long-standing position
that SV40 did not appear to be a health risk, federal officials decided to
convene a conference on the virus.
In January 1997, 30 scientists gathered at the National Institutes of
Health in Maryland. Garcea, Carbone and others presented their evidence
showing SV40 in tumors and pleaded for research funding.
Strickler presented his mesothelioma study, as well as new research he had
just completed, this time working with Fraumeni.
Their new study compared 20 years of cancer rates of people born between
1947 and 1963, and therefore likely to have been exposed to the
contaminated polio vaccine, with people born after 1963, who they believed
Their study found no significant difference between the two groups.
Letter of protest, 1998
But when Susan Fisher read Strickler and Fraumeni's study in the Journal of
the American Medical Association, she fired off a letter of protest to the
An epidemiologist at Loyola University Medical Center in Maywood, Ill.,
Fisher challenged the study's methodology, calling it "an error in
judgment" and misleading.
Using the same 20-year national cancer database for the two groups, Fisher
compared people of the same age - "because these cancers are highly
correlated with age" - and she came up with very different results.
Studying 18- to 26-year-olds who probably had been exposed to the
contaminated vaccine, Fisher found a 19.6 percent greater incidence of the
two major brain cancers linked to SV40 when compared with the incidence in
people the same age who were not exposed. She also found 16.6 percent more
bone cancers and 178 percent more mesotheliomas among those exposed to the
But Fisher cautioned against comparing the two groups. She argued that if
SV40 is being transmitted and circulating in the population, then many
people in the "unexposed" group would also be carrying the virus and that
would undermine the comparison.
Two types of SV40, 1999
For years, researchers had believed that all SV40-contaminated Salk vaccine
made between 1955 and 1963 had been used or discarded.
Then in 1999, Carbone was contacted by a former public health director in
Oak Park, Ill., who said he had seven sealed vials of vaccine dated October
1955 in a refrigerator in his basement.
Carbone, who had left the NIH and joined the faculty at Loyola University
Medical Center, ran tests on the vaccine and made a startling discovery:
Not only was the vaccine contaminated, it contained a second form of the
virus - an "archetypal" SV40 strain.
Although manufacturers switched from rhesus monkeys to SV40-free green
African monkeys to grow the bulk vaccine in 1961, they have continued to
use potentially contaminated polio seed strains originally grown on the
rhesus monkey tissue to start the bulk vaccine process.
Manufacturers check the purity of their vaccine with a series of 14-day
tests to detect whether any SV40 slipped through.
But when Carbone replicated the tests, he found that the second, slower-
growing "archetypal" strain took 19 days to emerge.
It was possible, Carbone noted in a published report, that this second
strain of SV40 had been evading manufacturers' screening procedures for
years - and infecting vaccine recipients after 1962.
Controversial study, 2000
Meanwhile, a new study led by Strickler had bogged down in bitter internal
After the NIH's 1997 conference, nine laboratories were recruited to
participate in a government-sponsored study to determine if tests were
really finding SV40 in tumors or whether earlier detections were the result
of laboratory contamination.
Carbone and other researchers considered the study unnecessary. A similar
multilab study led by Dr. Joseph Testa of Philadelphia had just been
completed, and it virtually eliminated the contamination theory. The
prestigious journal Cancer Research published Testa's findings in 1998.
But Strickler pressed on.
An independent laboratory in Maryland prepared mesothelioma samples for the
When tests revealed almost no SV40 in the tumor samples, some participants
questioned the preparation methods used by the Maryland lab. They also
challenged Strickler's written conclusion implying that contamination had
caused the earlier findings of SV40 in tumors.
If Strickler was right, the earlier SV40 detections were probably the
result of stray SV40 in the labs. But critics argued that the study was
scientifically flawed and should be scrapped.
The dispute became so contentious that FDA officials were forced to
intervene and a neutral arbitrator assigned to mediate.
Finally, in early 2000, more than two years after the study was initiated,
a carefully rewritten report emerged for publication.
It concluded that contamination was an unlikely explanation for earlier
SV40 findings. Then it struggled to explain the discrepancy between earlier
detections of SV40 in about half of all mesotheliomas tested and the fact
that the nine labs found the virus in only slightly more than 1 percent of
the study's tumor specimens.
The report noted that discrepancy might be because of the inefficiency of
the method used by the Maryland lab to recover DNA - like the genetic
sequences of SV40 - from the mesothelial tissue to create the test samples.
The Maryland lab also had inadvertently contaminated some of the laboratory
controls and "theoretically" could have contaminated others.
The report concluded by calling for further research.
Despite the study's ambivalent conclusions and technical problems, the NCI
submitted it to Cancer Research, the journal that had published Testa's study.
It was rejected.
Further discoveries, 2000
In laboratories around the world, researchers continued to find SV40 in a
widening range of tumors that now included pituitary and thyroid cancers
and some lymphomas.
Meanwhile, an NCI investigator named Dr. David Schrump was able to gut a
common respiratory virus and use it to deliver genetic material called
"antisense" into SV40-infected mesothelial cells and stop the cells'
His discovery, which was patented by the government, strongly suggested
that SV40 contributed to mesothelioma and that a treatment might be possible.
Then in August, Carbone and several colleagues published a major study
providing a "mechanistic" explanation of how SV40 contributes to the
uncontrolled growth of mesothelial cells. The key, they found, was the
large number of "tumor suppressor" proteins found in the mesothelial cells
that makes them unusually susceptible to SV40.
In most human cells, they said, the virus reproduces itself and kills the
infected cell in the process. But in mesothelial cells, SV40 is especially
attracted to the "tumor suppressor" proteins and binds to them, knocking
them out of action. The virus then lives on in the cell.
The result, they said, is a rate of malignant cell transformation in tissue
cultures 1,000 times higher than has ever been observed.
In a paper published in the Proceedings of the National Academy of Science,
Carbone further explained that asbestos fibers appear to act as a co-
carcinogen in mesothelioma by somehow suppressing the immune system's
response, which is designed to kill the infected cells.
Chicago conference, 2001
Carbone and others believed that the time had come for another conference
on the virus he calls "a perfect little war machine."
In April, more than 60 scientists gathered on a warm weekend at the
University of Chicago's downtown conference center. Despite numerous faxes
and certified letters inviting him, Strickler declined to attend.
Carbone opened the conference by confronting the question of whether SV40
is present in humans.
"Sixty-two papers from 30 laboratories from around the world have reported
SV40 in human tissues and tumors," he said. "It is very difficult to
believe that all of these papers, all of the techniques used and all of the
people around the world are wrong."
For two days, scientists from as far away as China and New Zealand
presented the results of their studies, with almost every speaker
concluding that SV40 was present in the tissues they examined.
One of the newest discoveries came from Dr. Jeffrey Kopp, an NIH scientist
who reported finding SV40 in a high percentage of patients with kidney
disease. The virus was also present, he said, in 60 percent of a new
"collapsing" type of renal disease that was unknown before 1980 but has
since increased rapidly in incidence.
There were also reports on efforts to develop a vaccine, recently funded by
the NCI, that would allow the immune system to target and eliminate SV40.
At times, the meeting took on almost revivalist overtones as scientist
after scientist said he or she was initially very skeptical of SV40's
presence in human tumors but was now a believer.
"I was a hard sell," said Testa, the Philadelphia geneticist who conducted
the first multilaboratory tests, noting that the study had convinced him.
Gazdar, the cancer researcher from Texas, showed a slide describing his
transformation: "Nonbeliever -- Believer - Zealot."
The conference concluded with a consensus among the leading scientists that
SV40's presence in human tumors was no longer in question. They were more
circumspect about the virus' possible role in causing cancer.
If SV40 is a human carcinogen, they said, the virus probably requires
interaction with other cancer-causing substances like asbestos.
Dr. Janet Butel from Baylor Medical College in Houston said that it simply
might be too soon to make a determination, citing the many years it has
taken to establish that other viruses cause cancer.
But even renowned tumor biologist George Klein from Sweden said he was
impressed by Carbone and Schrump's work.
"This strongly suggests that the virus plays a role (in causing tumors),"
said Klein, a former chairman of the Nobel Assembly.
Low priority, 2001
In May, shortly after the conference, Strickler's multilab study was
published in a small journal called Cancer Epidemiology, Biomarkers &
Carbone and other SV40 experts dismissed the study.
"A garbage paper in a garbage journal," said Garcea, now on the faculty at
the University of Colorado School of Medicine.
But Strickler strongly defends the study. He said it was the first to use
strict controls not used in other studies. He acknowledged, however, that
the study "doesn't prove that SV40 is not out there."
Strickler, who now teaches at Albert Einstein School of Medicine in New
York, said he remains skeptical about whether SV40 has infected humans, a
suspicion he says is shared by the broader scientific community.
But the NCI recently acknowledged that there is evidence to suggest that
SV40 "may be associated with human cancer." The NCI statement, released
last month, also said that SV40's interaction with "tumor suppressor
proteins" indicates "possible mechanisms that could contribute to the
development of cancer."
Top NCI officials declined to be interviewed on the record for this report.
Fraumeni also declined several requests for an interview.
Dr. James Goedert, the chief of the NCI's Viral Epidemiology Branch who
supervised Strickler's work, said that if SV40 is in human tumors, it must
be at extremely low levels. To critics who claim the government has
downplayed SV40's potential health risks, Goedert responded: "Absolutely not."
He acknowledged that research is needed to resolve the question of whether
SV40 is prevalent in the human population and, if so, how it might be
spreading. But Goedert said he has no plans for such studies.
"It's not our highest priority," he said.
Key figures in developing vaccines and tracing SV40
Dr. Jonas Salk Developed the first polio vaccine using killed virus in 1955.
Virologist Albert Sabin Developed an oral vaccine using weakened live virus.
Dr. Robert Garcea Used new technology to trace SV40 in children's brain
Q&A on polio vaccine contaminated with SV40 Q: How widespread is the SV40
A: Scientists and government health officials don't know because no
comprehensive studies have addressed the question.
What is known: During the 1950s and '60s, more than 100 million people
worldwide were given SV40-contaminated polio vaccine. The virus also has
been found in people who did not receive contaminated vaccine, as well as
laboratory workers and monkey handlers. No studies, however, have examined
how SV40 might be transmitted between people, or if somehow humans might
have become infected with SV40 before the introduction of the tainted
Q: Can I be tested for SV40?
A: An accurate blood test does not exist. Current antibody blood tests can
be inaccurate, scientists say, because they may also detect the presence of
other closely related viruses, and SV40 may be present at such a low level
that no antibodies are produced. Researchers are working to create an
Q: Is the current
polio vaccine safe?
A: Vaccine producers, health officials and most scientists believe that it
is safe. Manufacturers say they take elaborate steps to test their vaccine
for SV40, and the government says it recently tested vaccine samples back
to 1972 and found no trace of SV40.
Some scientists, including Dr. Michele Carbone, have raised questions about
whether manufacturers' testing techniques have been adequate. Carbone,
however, tested vaccine from 1996 and found no SV40. He has had his
Q: In which kinds of cancers has SV40 been found?
A: The virus has been detected in rare cancers:
-- Mesothelioma, a fatal tumor of the membrane surrounding the lungs. Few
cases were reported prior to 1950, but the incidence has grown in the
United States to 2,000 to 4,000 cases a year, with greater incidence in
-- Brain cancers: Primarily ependymoma and choroid plexus tumors, but also
astrocytoma, glioblastoma, medulloblastoma and meningioma. These make up a
total of less than 1,000 U.S. cases each year.
-- Bone cancers: Primarily osteosarcoma but also chondrosarcoma and giant
cell tumors. These also make up less than 1,000 cases annually.
-- Other cancers: A few detections in pituitary and thyroid tumors and
The sources for this report include the books "The Saga of Jonas Salk" by
Richard Carter and "The Health Century" by Edward Shorter; articles in
Atlantic Monthly and New York magazine; newspaper archives at The Chronicle
and the New York Times; transcript of the 1997 National Institutes of
Health Conference in Bethesda; a review of dozens of scientific journal
articles and scores of interviews.
Related series: Quest for the Origin of AIDS.
How SV40 contaminated polio vaccine
When Dr. Jonas Salk introduced the first polio vaccine in 1955, it was
hailed as "one of the greatest events in medicine." Within 10 years, U.S.
polio cases plummeted from 30,000 to less than 1,000. But in 1960, a monkey
virus called SV40 was found in the Salk vaccine. As much as one-third of
the vaccine was contaminated. SV40 was also found in earlier versions of an
oral vaccine developed by Dr. Albert Sabin that replaced the Salk vaccine
in the 1960s. When it was discovered that SV40 caused cancer in lab
animals, U.S. health officials ordered vaccine manufacturers in 1961 to
eliminate the virus from all future vaccine, although questions remain
about whether they succeeded with the Sabin vaccine. .
Making the Sabin vaccine: 1955-1961 Starting in the mid-1950s, both Sabin
and Salk vaccines are made by growing polio virus on kidney tissue from
Asian rhesus monkeys, which are natural hosts for the simian virus known as
SV40. Special weakened seed strain of polio virus developed by Sabin is
grown on rhesus kidney tissue to make large bulk amounts of vaccine. SV40
from the kidney tissue contaminates the vaccine. .
Making the vaccine safe: 1961 In 1961, after SV40 is discovered in the
vaccines, U.S. health officials order manufacturers to eliminate SV40.
Antiserum is used to neutralize SV40 in seed stock, and SV40-free African
green monkeys are used to grow bulk vaccine. But some researchers believe
small amounts of SV40 may have survived. .
Testing Manufacturers check the safety of the vaccine pools by using a
series of 14- day growth tests to see if SV40 is present.
Making the Salk vaccine: 1955-1961 Full strength polio virus is grown on
rhesus kidney to make bulk Salk vaccine. SV40 from the kidney tissue
contaminates the vaccine. The polio virus is then killed with formaldehyde,
but some SV40 survives. .
Making the vaccine safe: 1961 In the original vaccine, the SV40 survives,
contaminating up to 30 million Americans. But after 1961, African green
monkeys are used to grow bulk vaccine and SV40 is eliminated.
Sources: Children's Hospital of Philadelphia; SEER; virus images by Jean
Yves Sgro, University of Wisconsin; Chronicle research
For more information about the simian virus SV40, the following studies or
scientific reviews were published during that past year:
A multicenter evaluation of assays of detection of SV40 DNA and results in
masked mesothelioma specimens. Strickler H, Goedert J., Cancer
Epidemiology, Biomarkers & Prevention. Vol. 10, 523-532, May 2001.
Simian virus 40 and human cancers, Strickler H., Einstein Quarterly J.
Biol. and Med. (2001) 18:14-21. This includes a detailed bibliography that
will lead readers to earlier scientific articles.
Oral polio vaccine and human cancer: a reassessment of SV40 as a
contaminant based upon legal documents. Kops S., Anticancer Research (2000)
Human mesothelial cells are unusually susceptible to SV40-mediated
transformation and asbestos cocarcinogenicity. Bocchetta M, Di Resta I,
Powers A, Fresco R, Tosolini A, Testa J, Pass H, Rizzo P, Carbone M., Proc.
Natl. Acad. Sci. USA, Vol. 97, Issue 18, 10214-10219, Aug. 29, 2000.
In addition, a bibliography of journal articles by leading SV40 researcher
Dr. Michele Carbone can be viewed by clicking on the following link: