WASHINGTON -- Flu season in the United States is having its earliest start in nearly a decade, and health officials say this season could be a bad one.
Although flu is always unpredictable, the early nature of the cases and the predominant type circulating this year could make this a severe flu season, said officials at the Centers for Disease Control and Prevention.
But officials said the vaccine formulated for this year is well-matched to the strains of the virus seen so far and urged those who have not been vaccinated to get a flu shot.
In early December, the CDC said it was noticing an uptick in flu activity about a month before authorities normally see it, and the earliest since the 2003-04 flu season. The primary strain this season is the H3N2, an influenza A virus that has been associated in the past with more severe flu seasons.
Since the beginning of December, "there has been increasing influenza activity in more parts of the United States and more cases of flu," said Joe Bresee, chief of epidemiology at CDC's influenza division, in an interview last week. "We have seen increasing trends that flu is increasing in the last few weeks of the year, and I wouldn't be surprised if we see that continue into the new year."
Influenza often peaks in January, February or even later.
Cases of flu have been reported in 29 states. As of Dec. 15, higher-than-normal reports of flulike illnesses had been reported in 12 states, most of them in the South and Southeast: Virginia, Alabama, Georgia, Louisiana, Mississippi, Missouri, North and South Carolina, Tennessee, Texas, Illinois and Utah.
Based on data from the past two decades, during the years when H3N2 is the predominant flu strain, "there are more deaths and hospitalizations," Dr. Bresee said.
It is not completely clear why. One factor may be that the elderly, who are at high risk for flu complications, tend to become sicker with the H3N2 strain than the other two common flu strains, he said.
But this flu season offers two bits of good news, as well.
Of the flu strains that are spreading this year, about 80 percent are the influenza A type, and almost all of those are the H3N2 strain, Dr. Bresee said. That matches well with this year's flu vaccine, which includes the H3N2 strain.
On average, about 25,000 Americans die each flu season, according to the CDC.