Some two-thirds of the 3,700 laboratories worldwide that received samples of a killer flu virus in test kits have destroyed them as instructed, the World Health Organization (WHO) said on Friday.

Most of the labs are in the United States, but the rest are scattered in 17 countries, 12 of which have replied that they had disposed of their samples, according to Klaus Stohr, head of the WHO’s influenza program.

“Two-thirds of this material has been destroyed and the rest of the material is also hopefully subject to destruction very fast,” he told a news conference in Geneva.

However, the United Nations agency was still investigating what had happened to samples listed as having gone to two laboratories in Mexico and Lebanon.

The virus did not arrive at either place, but it may never have been sent, Stohr said.

The U.S. College of American Pathologists (CAP) distributed the virus, starting in October last year, as part of routine testing of laboratories’ ability to detect strains.

Although it was legal to use the “Asian” H2N2 flu virus, which killed between one and four million people in 1957, the WHO said it was an “unwise” choice for such tests.

It has called for the bug to be put on a higher security rating so that laboratories take even more precautions when handling it.

So far there have been no reports of any infections and the fact that laboratories are used to handling such things means that the chances of its escaping into the community are remote, according to the WHO.

NO ANTIBODIES

The virus is the only old influenza bug still kept in laboratories and to which most people would have no antibodies. But back in 1957, it mainly attacked the elderly, and those in that age group now would still have some immunity.

The 12 countries to notify the WHO that they had destroyed samples were Belgium, Canada, Chile, France, Germany, Hong Kong, Italy, Lebanon, Mexico, Singapore, South Korea, Taiwan.

The five remaining countries were Bermuda, Brazil, Israel, Japan, and Saudi Arabia, all of whom had “good infrastructure,” Stohr said.

“We are not worried about any of these countries,” he added.

The official said that he was confident that all laboratories outside the United States would have completed destruction of the virus within the next few hours, but the situation was less clear in the United States.

“For international laboratories (non-U.S.), we are relatively confident that the exercise can be accomplished by close of business tonight,” Stohr said. “That is our goal.”

“For the United States, it remains to be seen, it is a large task. But everything is on the right track,” he added.