The U.S. flu season is getting worse. And U.S. health officials in Atlanta say it's partly because the flu vaccine doesn't match most of the circulating viruses.
Infections from an unexpected flu strain have been booming.
Scientists at the U.S. Centers for Disease Control and Prevention say the current vaccine is a good match for only about 40 percent of the spreading flu viruses.
This week, 44 states reported widespread flu activity, up from 31 last week.
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