Flu pandemic fears after blunder

A lethal flu virus has been accidentally sent to thousands of laboratories around the world.

Experts fear the strain could cause a global pandemic among those under 36 who have no immunity to it.

The virus originally appeared in 1957 and is believed to have killed about four million people before being eradicated by 1968.

However, the strain has not been included in flu jabs since 1968. "If this virus gets loose, it can easily cause an influenza epidemic," Dr Klaus Stohr of the World Health Organisation said. "If this were to infect one person, it would spread very rapidly."

Almost 4,000 laboratories in 18 countries were sent the flu virus after samples were accidentally included in testing kits.

It is feared that if a lab worker became infected, the virus could quickly spread through the general population.

"The risk is relatively low that a lab worker will get sick, but a large number of labs received the virus and if someone gets infected, the risk of severe illness is high. This virus has been shown to be fully transmissible," said Dr Stohr.

"Things can go wrong as long as these samples are out there and there are some still out there."

It was not immediately clear why the 1957 pandemic strain was in the proficiency test kits routinely sent to labs. Dr Stohr described the mistake as "unfortunate".

The kits are used for internal quality control checks to demonstrate that a lab is able to identify viruses, or as a way for labs to become certified by the College of American Pathologists, which sent the samples.

Most of the laboratories that received kits are in the US, according to the WHO. Fourteen were in Canada and 61 samples were sent to 16 countries in Europe, Asia, the Middle East and South America.

The company has written to the laboratories affected, which have not been named for security reasons, and hopes they will have destroyed the vials by the end of the week.

However, the WHO warned that the test kits are not the only supplies of the 1957 pandemic strain in laboratories. "The world really has to think what routine labs should be doing with these samples they have in the back of their fridges," Dr Stohr said.

Experts fear the flu strain could be used for bio-terrorism if it fell into the wrong hands. The WHO delayed publicising the mistake until all the affected laboratories were informed, in a bid to avoid alerting terrorists.

Dr Stohr said the company had acted in compliance with US regulations, which are being revised.

Flu jabs have not contained the strain in question since 1968, meaning that only people given the injection before 1968 would be protected. Flu jabs include a small amount of the virus, which triggers the immune system into producing antibodies to protect against the disease.