The Chronicle reported last week that the simian virus SV40 had contaminated early polio vaccine given to millions of Americans. When health officials discovered in 1961 that SV40 caused malignant tumors in lab animals, they ordered the virus eliminated from all future vaccine.

But internal memos from Lederle Laboratories, the chief producer of polio vaccine in the United States, indicate SV40 may not have been completely removed.

According to one memo, SV40 was found in three of 15 lots of the oral vaccine seven months after the federal directive was issued in March 1961. Lederle released the contaminated vaccine to the public anyway, the memo shows.

The documents also suggest that the company failed to test the monkey- kidney seed strains used to make the bulk polio vaccine for contamination, despite a written warning from Dr. Albert Sabin, who developed the oral vaccine.

Lederle and the U.S. government insist there is no evidence that any contaminated vaccine was distributed after the directive went into effect.

Scientists discovered SV40 in the Salk polio vaccine in 1960. By then as many as 30 million Americans had been given injections of the SV40-tainted polio vaccine, which was first licensed in 1955.

In recent years more than 60 scientific studies have found SV40 in rare human brain, bone and lung-related cancers, the same kinds of tumors the virus caused in laboratory animals. Some scientists believe SV40 may play a role in causing those cancers.

One of the biggest mysteries, however, is why SV40 has been found in tumors removed from people who never received the contaminated Salk vaccine.

Researchers have several theories for how the virus could have spread from those infected through the Salk vaccine: in transmission from mother to fetus or through breast milk; through sexual activity or a flu-like virus.

But the Lederle documents, which were obtained by Philadelphia attorney Stanley Kops in litigation not related to SV40, raise the possibility the virus might have been transmitted by contaminated oral vaccine, licensed for production in 1962.

The documents include:

-- A November 1961 memo saying the virus was found in three of 15 lots of vaccine. According to the memo, Dr. Roderick Murray, head of the government's program to ensure vaccine purity, allowed the lots to be released.

To comply with the removal order, Lederle had switched from rhesus monkeys, which are natural hosts for SV40, to African green monkeys, supposedly free from SV40. However, the memo notes that SV40 was found in 10 percent of the green monkeys.

-- A letter from Sabin to Lederle in October 1962, warning that sufficient testing for SV40 contamination had not been done on one of his strains of weakened polio virus that formed the seed for bulk vaccine production.

-- A confidential memo in 1979 from a Lederle official stating: "It should be noted that Lederle did not test the original Sabin seeds for extraneous agents or neurovirulence since Dr. Sabin assured us that this had been done."

-- Another memo stating that Lederle did not test the seed "since only 50 (milliliters) or less of each seed were provided by Dr. Sabin."

The two memos added that testing was unnecessary because later vaccine samples submitted for license were free of SV40.

Kops also said that he had taken testimony in 1998 from a top Lederle official who said the company did not have the test results from many of the vaccine lots.

"The vaccine manufacturers and the government need to disclose what really happened," said Kops. "Without the facts, (scientists) will continue to look in the wrong places to explain how people were infected with SV40 after 1961."

Lederle did not respond to requests for comment.

At a 1997 conference, however, a company representative outlined the series of tests the company uses to detect SV40 contamination. The company also says that it uses antiserum to neutralize any SV40 in the "master seeds."

But it is not clear whether these procedures were in place in the years after the U.S. government issued its directive.

Last year, a lawsuit was filed in Los Angeles against Lederle by the parents of 2 1/2-year-old Alexander Horwin who died of a brain tumor that later tested positive for SV40. The suit claims that the tumor was caused by SV40 and that he became infected through a 1997 oral polio vaccine.

Kops and attorney Donald MacLachlin represent a New Jersey family that is considering a suit against vaccine manufacturers.

In 1970, surgeons removed a large brain tumor from 2-year-old Mark Moreno. He since has undergone five more surgeries and now wears a protective helmet over the large opening in his cranium where bone grafts never took. Moreno, now 33, lives with his mother and requires daily assistance.

Recent tests show Moreno's tumor was riddled with SV40, according to the lawyers.

Eileen Moreno, Mark's mother, believes her son's brain tumor was caused by SV40 and that he was infected through the oral polio vaccine in 1968.

Last year, two investigators from the U.S. Food and Drug Administration used genetic testing to examine 30 samples of bulk oral polio vaccine used in the United States going back to 1972. They reported finding no SV40.

But the government has not used the genetic tests to determine whether vaccine made prior to 1972 was contaminated.

Dr. William Egan, deputy director of the FDA's vaccine research branch, said testing went back only to 1972 because those samples were the only ones available to them. "There was nothing sinister," he said.

MacLachlin said he finds it "incredible" that the government hasn't comprehensively investigated the possibility of SV40 contamination of the oral vaccine.

Simian virus Q&A Q

How widespread is the SV40 infection?

A: Scientists and government health officials don't know, because no comprehensive studies have addressed the question. What is known is that during the 1950s and '60s, at least 10 million to 30 million Americans -- and 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.

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 also may detect the presence of closely related viruses, and SV40 may be present at such a low level that no antibodies are produced. Researchers are working to create an effective test.

Q: In which kinds of cancers has SV40 been found?

A: The virus has been detected in rare cancers, including:

-- 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 Europe.

-- Brain cancers: Primarily ependymomas and choroid plexus tumors, but also astrocytomas, glioblastomas, medulloblastoma, and meningiomas. Fewer than 1, 000 cases of these cancers are reported in the United States each year.

-- Bone cancers: Primarily osteosarcomas, but also chondrosarcoma and giant cell tumors. These also make up fewer than 1,000 cases annually. ___

For more information on SV40 and the polio virus, please check the Internet at sfgate.com/chronicle/sv40/

http://www.sfgate.com/cgi-bin/article.cgi?file=/c/a/2001/07/22/MN173141.DTL