And the FDA panel on Thursday followed the WHO lead. The new flu strains include Brisbane/10, a version of the H3N2 flu; a second new Type A strain known as H1N1/Brisbane/59, and a newer Type B/Florida strain.
The virus strain most common in the United States right now is the influenza A H3N2 strain, and it's a strain not included in this year's vaccine. Also, this year's vaccine is not well-matched against influenza type B.
Complicating matters, some of this year's influenza type A virus is showing resistance to the antiviral drug Tamiflu. Overall, 8.1 percent of the influenza type A viruses tested by the CDC were resistant to Tamiflu. In past years, less than 1 percent of the viruses have been resistant to the drug.
The composition of a flu vaccine is not an easy prediction at best, Welch said.
"Although these are educated guesses, they clearly are guesses," he added. "Sometimes, they guess right. Sometimes, they guess wrong. This year, they didn't guess well. Sixteen out of the last 19 years they have guessed pretty well."
For the week ending Feb. 9, widespread flu activity was reported by 44 states and regional activity was reported by five, for a total of 49, according to the CDC's latest tally. During the three most recent flu seasons, the number of states reporting regional or widespread activity peaked at 41 to 48 states.
Ten children, ranging in age from 4 months to 14 years, have died from influenza so far this year, the CDC also reported. During the last three years, flu-related deaths among children have ranged from 46 to 74.
Even though this year's vaccine isn't a good match for most of the circulating flu virus, CDC officials continue to recommend that people g
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