These strains haven't evolved or mutated and are the same strains that have been circulating for the past few years, Bresee said. They also match the strains included in the flu vaccine over the past two years.
Good vaccination coverage may be playing a role in flu's relative inactivity this year. "We have had very high vaccination rates in the last couple of years, and that probably dampens the amount of flu," Bresee said. "The underlying immunity of the population is probably higher than it usually is to the viruses we are seeing."
"But there are a lot of things that play into it, most of which we don't understand but are thankful for," Bresee added.
And does the late arrival of the flu herald its early departure this year? "It's hard to know if the late start to the flu season means that it will go on longer," Bresee said.
"We are getting a late start, but we don't know when the peak will be, if it will be a lower peak or a normal peak," he said. "We always can predict after the year is over, sadly."
"So, the good news is that because of the late start, folks who haven't been vaccinated still have a chance to do so," Bresee said. "Since we are seeing a late start, most communities have the opportunity to get vaccinated ahead of the flu season."
Everyone aged 6 months and older should get a flu shot, according to the CDC.
For more on the flu, visit the U.S. Centers for Disease Control and Prevention.
SOURCES: Joseph Bresee, M.D., chief, epidemiology and prevention branch, influenza division, U.S. Centers for Disease Control and Prevention; Feb. 24, 2012, Morbidity and Mortality Weekly Report
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