Scientists around the world were scrambling today to prevent the possibility of a pandemic after it emerged that a deadly influenza virus had been sent out to thousands of laboratories.
The scare was prompted after US firm Meridian Bioscience, sent out the H2N2 virus - similar to one associated with the 1957 Asian flu pandemic that killed up to four million people - in routine testing kits to almost 5,000 laboratories in 18 different countries.
All laboratories that have received the H2N2 virus were urged by the World Health Organisation (WHO) to destroy the samples because of the slight risk they could trigger a global outbreak.
Klaus Stohr, who coordinates the WHO global influenza programme, said sending out the virus had been "unwise".
There are no reports of anyone being infected and Mr Stohr said the risks were low, but he added that "if someone does get infected, the risk of severe illness is high, and this virus has shown to be fully transmissible".
Most of the affected labs are in the US and Canada. The UK's health protection agency said it was "highly unlikely" the virus had been sent to the UK, although it has been sent to at least four European countries - France, Germany, Italy and Belgium.
A spokeswoman for the health protection agency, which covers England and Wales, said: "We're not aware of any of these vials being sent to UK labs."
Meridian, based in Cincinnati, Ohio, had decided to use the H2N2 virus in testing kits as one of the blind samples that labs must correctly identify to acquire certain certifications.
Usually the influenza virus included in the kits is one that is currently circulating or has recently circulated. The H2N2 virus has not been included in flu vaccines since 1968, and anyone born after that date will have little or no immunity to it.
A Canadian laboratory detected the 1957 pandemic strain on March 26 in a sample that was later traced to a test kit.
US health officials said they had learned on Friday last week that test kits prepared by Meridian contained the virus. Dr Nancy Cox, the head of the influenza branch at the Centres for Disease Control and Prevention, said: "The risk is low and we've taken appropriate action."
But the virus's presence in thousands of labs has focused fresh attention on the safe handling of deadly germs, an issue that led to tougher rules in the US after anthrax was sent in the post in 2001, killing five Americans.
Dr Cox said officials strongly doubted that someone deliberately planted the dangerous germ. "It would not be a smart way to start a pandemic to send it to laboratories, because we have people well trained in biocontainment," she said.
Mr 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," Mr Stohr said.
Meridian reportedly chose the H2N2 virus from a "germ library" in 2000.
The company makes kits for at least four groups that help labs do proficiency testing. The largest of these, the College of American Pathologists (Cap), confirmed that by February it had forwarded more than 3,000 kits to other labs.
The labs concerned have been asked to incinerate the samples immediately and confirm their actions in writing.
Other countries affected by the scare are Bermuda, Brazil, Canada, Chile, Hong Kong, Israel, Lebanon, Mexico, South Korea, Saudi Arabia, Singapore and Taiwan.
The latest scare comes at a time when scientists have been warning of the threat of a flu pandemic if an Asian strain that affects birds were to mutate and become easily transferred to humans.
