WHO: Deadly Bird Flu Virus Can Mutate

The deadly H5N1 strain of bird flu which has killed at least 148 people is showing signs of being able to mutate and develop resistance to the most effective anti-viral drugs and any possible vaccines yet to be produced, a WHO scientist said Thursday.

The H5N1 virus is splitting into genetically different groups, said Mike Perdue, a team leader with WHO's influenza program who took part in a two-day bird flu conference earlier this week sponsored by the U.N. health body.

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No vaccine for the H5N1 virus has been produced yet, but scientists are confident they will develop one in future.

However, the virus has now been shown to mutate like seasonal flu viruses that require new vaccines every year. "We are going to have to come to the realization that these viruses are genetically variable," Perdue said. "The vaccines that we have predicted to be protective today may not be protective a year from now."

The two most effective anti-viral drugs currently in use are also in danger of losing their potency, according to influenza experts.

"We know from surveillance studies and from hospital clinical studies that resistance to the two primary anti-viral drugs, the Tamiflu and Amantadine drugs, have already occurred," Perdue said.