ATLANTA — This winter's most prevalent influenza strain is showing signs of "drifting" toward a new flu that the current vaccine is not designed to handle, federal researchers said Thursday.
The Centers for Disease Control reported that Type B flu viruses seen in Michigan and Georgia apparently are different from the last major Type B strain to circulate in this country, known as the U.S.S.R. flu.
The flu vaccine now being given protects against the U.S.S.R. flu because it was the Type B strain seen a year ago, when this winter's flu vaccines were being developed.
New Vaccine Impossible
It would be impossible to get a vaccine to the public this winter to protect against a new flu, CDC scientists said.
It is not known exactly how the new strains are evolving, how widespread the new flu might be or how effective the vaccine might be against the Michigan and Georgia viruses.
Scientists currently are planning next winter's flu vaccine, which likely will include protection against a new strain, said Dr. Karl Kappus, a CDC flu specialist.
He said researchers still don't know what strain--or strains--may be evolving. "This hasn't been worked out enough to talk about this sort or that sort or a third sort," Kappus said. "That's what we're doing right now."
Major Flu Strains
There are three major groups of flu strains, which scientists know as A-H3N2, A-H1N1 and B. Flu viruses, especially rapidly evolving Type B viruses, are always changing, Kappus said.
But the latest shift in Type B flu has come more rapidly than usual, Kappus said.