"The swine flu virus contains sets of genes that make neuraminidase, a viral protein involved in replication, and matrix, a structural protein, which had never been seen outside of Asia before, CDC researchers said in one of the studies. The strain's sudden appearance may indicate a gap in flu surveillance, said Michael Shaw, a CDC microbiologist.

'A lot of researchers are going back to their freezers to see if there's anything they've overlooked, in earlier flu samples, he said today on the conference call."

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