The rush, urged by the World Health Organization, was sparked by a slim, but real, risk that the samples, could spark a global flu epidemic. The vials of virus sent by a U.S. company went to nearly 5,000 labs, mostly in the United States, officials said.
"The risk is relatively low that a lab worker will get sick, but a large number of labs got it and if someone does get infected, the risk of severe illness is high and this virus has shown to be fully transmissible," WHO's influenza chief, Klaus Stohr, told The Associated Press.
It was not immediately clear why the 1957 pandemic strain, which killed between 1 million and 4 million people — was in the proficiency test kits routinely sent to labs.
It was a decision that Stohr described as "unwise," and "unfortunate."
That particular bug was "an epidemic virus for many years," Stohr said from the U.N. health agency's headquarters in Geneva, Switzerland. "The risk is low but things can go wrong as long as these samples are out there and there are some still out there."
The 1957 strain has not been included in the flu vaccine since 1968, and anyone born after that date has no immunity to it.
Dr. Nancy Cox, chief of the influenza branch at the federal Centers for Disease Control and Prevention in Atlanta, said her agency was notified of the situation Friday morning. She also said officials strongly doubt someone deliberately planted the dangerous germ or that this was an act of bioterrorism.
"It wouldn't be a smart way to start a pandemic to send it to laboratories because we have people well trained in biocontainment," she said.
The concern over the shipment of pandemic flu virus to thousands labs renews questions about the safe handling of deadly germs — an issue that led to toughened U.S. rules after anthrax was sent in the mail in 2001, killing five Americans.
Most of the flu samples — 3,747 — were sent starting last year at the request of the College of American Pathologists, which helps labs do proficiency testing. The last shipments were sent out in February.
Dr. Jared Schwartz, an official with the pathology college, said a private company, Meridian Bioscience Inc. of Cincinnati, Ohio, is paid to prepare the samples. The firm was told to pick an influenza A sample and chose from its stockpile the deadly 1957 H2N2 strain.
Stohr said U.S. health officials also reported to WHO that some other test kit providers besides the college used the 1957 pandemic strain in samples sent to labs in the United States. Schwartz identified them as Medical Lab Evaluators, the American Association of Bioanalysts and the American Association of Family Practitioners.
Almost 99 percent of the labs that got the test kits are in the United States, Stohr said. Fourteen were in Canada and 61 samples went to labs in 16 other countries in Europe, Asia, the Middle East and South America, according to the WHO.
Some of the labs outside the United States have already destroyed their samples, he said, and WHO is hoping that the rest of the vials will be destroyed by Friday. The health agency wouldn't name the other countries whose labs received the samples.
The test kits are used for internal quality control checks to demonstrate that a lab is able to correctly identify viruses or as a way for labs to get certified by the College of American Pathologists.
The kits involve blind samples. The lab then has to correctly identify the pathogen in the vial in order to pass the test. Usually, the influenza virus included in these kits is one that is currently circulating, or at least one that has recently been in circulation.
On March 26, National Microbial Laboratory Canada detected the 1957 pandemic strain in a sample not connected with the test kit. After informing WHO and the CDC of the strange finding, the lab investigated. It informed the U.N. health agency on Friday that it had traced the virus to the test kit.
The WHO then notified the health authorities in all countries that received the kits and recommended that all the samples be destroyed immediately.
That same day, the College of American Pathologists faxed the labs asking them to immediately incinerate the samples and to confirm in writing that the operation had been completed.
Stohr said the test kits are not the only supplies of the 1957 pandemic strain sitting in laboratories around the world.
"The world really has to think what routine labs should be doing with these samples they have kept in the back of their fridges," Storh said.
Viruses are classed according to the level of lab safety precautions that must be taken when handling them. Routine viruses can be handled in labs with a basic level of biosafety protection. However, very dangerous viruses, such as Ebola, can only be handled at labs with top-level safety measures. Those labs have a biosafety level of 4.
The 1957 flu virus has for years been a level 2 virus, but many countries have upgraded it to a biosafety level of 3 because so many people have no immunity to it. Stohr said U.S. officials reviewing the classification and are expected to increase it to a level 3 later this summer.