Thousands of scientists worldwide are destroying vials of a pandemic flu strain over concerns the samples could set off a global flu epidemic.

Samples of a strain that was responsible for a flu epidemic in 1957 was inadvertently included in kits that are routinely sent to laboratories around the world by the College of American Pathologists to test their proficiency.

The World Health Organization said the vials were sent starting last fall and went to nearly 5,000 labs -- mostly in the United States. Some also went to Canada and Mexico.

More than 60 laboratories outside North America also received them, including labs in Belgium, Bermuda, Chile, Brazil, France, Germany, Chile, Hong Kong, Israel, Italy, Japan, Lebanon, South Korea, Saudi Arabia, Singapore and Taiwan.

The WHO said Canada, South Korea, Hong Kong and Singapore had already destroyed their samples, while Japan was doing the same. Taiwan and Germany also announced that they had destroyed all their vials.

In the United States, inventory is being taken by the College of American Pathologists, and Dr. Julie Gerberding, the director of the Centers for Disease Control and Prevention, said most labs have destroyed their vials.

"In the future, we will be urgently recommending that a higher level of precaution be used in any novel strain of flu virus." - Dr. Julie Gerberding, CDC Director

The germ, the H2N2 "Asian flu" strain, killed between 1 million and 4 million people in 1957. It has not been included in flu vaccines since 1968, and anyone born after that date has little or no immunity to it.

"While the risk of the situation is very low, we're not taking any chances," Gerberding said at a Wednesday news conference. "Our concern is that our population does not have immunity" to the virus.

The investigation is continuing as to why the dangerous strain was included in the test kits, which were created by Meridian Biosciences Inc. Gerberding said the company created the kits knowing the H2N2 virus was included.

The kits contain blind samples that labs must correctly identify to pass the test. The influenza virus included in the kits is usually one that is currently circulating or has recently circulated.

A Canadian laboratory detected the 1957 pandemic strain on March 26 in a sample that was later traced to a test kit. The lab told the WHO about the discovery last week, at which point the agency recommended the samples be destroyed.

The same day, the College of American Pathologists faxed the labs, asking them to incinerate the samples and confirm that in writing.

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For now, Gerberding said labs that received the virus should destroy the samples, monitor their workers, and test anyone who has been exposed to the virus for influenza. But she emphasized that there's no evidence that anyone has been exposed.

Klaus Stohr, the WHO's influenza chief, called the decision to send out the virus "unwise."

Stohr said the risk of a lab worker getting the flu "is relatively low." But he said if a large number of labs got the samples and somebody did get infected, "the risk of severe illness is high."

Viruses are classified 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.

"In the future, we will be urgently recommending that a higher level of precaution be used in any novel strain of flu virus," Gerberding said.

Gerberding said only the most secure labs should handle vials of flu virus. She said the government should restrict the number of labs with access to the virus. She says her agency has already recommended that change, but it hasn't happened yet because the flu has never been considered a possible bioterror weapon.

World Health Organization Statement
College of American Pathologists Statement
Centers for Disease Control and Prevention

Previous Story:

• April 13, 2005: WHO Identifies All Countries That Got Killer Flu Virus
• April 12, 2005: Scientists Scramble To Destroy Pandemic Flu Vials