Feb. 24, 2012 -- Flu season is officially under way, the CDC says.
It's the latest start in 24 years, Joseph Bresee, MD, chief of epidemiology and prevention at the CDC's flu branch, said at a news teleconference.
The CDC declares a flu season when for three weeks in a row at least 10% of people seeing a doctor for flu-like symptoms actually test positive for flu. The CDC has done this for 29 years. Only once before, in the 1987-88 flu season, has it come so late in the year.
"Flu viruses have been reported from all 50 states," Bresee said. "Fortunately, because flu activity remains relatively low, levels of severe flu are low."
Currently, flu activity is highest in the Midwest, with high-level activity in Missouri.
Three children have died of flu during this 2011-2012 season. The annual number of child flu deaths ranges from 46 to 202 during flu seasons. The 2009 H1N1 pandemic killed 340 children.
Even though it's been a mild flu year so far, look out: Over the last 35 years, U.S. flu has surged four times in March and twice in April.
Why such a late and (so-far) mild flu season? Flu is hard to predict, but Bresee offered several possible reasons:
The flu bugs circulating this year are very much the same as those from last year. There may be a higher-than-usual level of flu immunity in the U.S. this year.
More people than ever before are getting their flu shots -- and this year's flu vaccine is a good match for this year's flu. About 132 million doses of flu vaccine were distributed this year.
The weather has been warmer in much of the U.S. Flu bugs spread better in cold, dry air. And when it's really cold out, people huddle together indoors, spreading germs.