A dangerous strain of the flu virus that caused a worldwide pandemic in 1957 was sent to thousands of laboratories in the United States and around the world, triggering a frantic effort to destroy the samples to prevent an outbreak, health officials revealed on Tuesday. Because the virus is easily transmitted from person to person and many people have no immunity to it, the discovery has raised alarm that it could cause another deadly pandemic if a laboratory worker became infected, officials said. As a result, health authorities were urgently working to make sure all samples are destroyed and to closely monitor anyone who may have come into contact with the virus for signs of illness, officials said.‘‘This virus could cause a pandemic,’’ said Klaus Stohr, the World Health Organisation’s top flu expert. Although no infections have been reported, and the chances of infection are probably low, the potential consequences are so grave that urgent steps were necessary, he said. ‘‘If a laboratory accident were to occur, a person could become infected. If that happened, that person would likely fall ill and he or she could infect somebody else. And that could mark the beginning of a global outbreak,’’ Stohr said.WHO is working with the federal Centers for Disease Control and Prevention in Atlanta and other national health agencies to contain the situation, he said, adding, ‘‘the level of concern about this virus is very high.’’ The virus, known as an H2N2 strain, killed 1 million to 4 million people worldwide in 1957 and 1958, including about 70,000 in the United States. Because the virus has not circulated in the wild since 1968, anyone born after that would have no natural immunity to it. —LAT-WP
