The World Health Organization says it is investigating samples of mutated swine flu found in two Norwegians who died of the virus and one person who suffered severe illness.Norway's Institute of Public Health announced Friday that the mutation "could possibly...cause more severe disease" because it infects tissue deeper in the airway than usual.
But the global body says the same mutation has been found in mild cases while samples from other deaths around the world didn't contain the variant strain.
WHO says "the public health significance of this finding is thus unclear."
Some 680,000 Norwegians are estimated to have been infected with swine flu to date, of which 23 have died.
WHO says there have been over 6,750 deaths worldwide so far.
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