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 they 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, the earliest since the 2003-2004 flu season. The primary strain this season is 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 CDCs influenza division.
Flu usually peaks in midwinter, and symptoms can include fever, cough, runny nose, head and body aches, and fatigue. Some people also suffer vomiting and diarrhea, and some will develop pneumonia or other severe complications.
On average, about 25,000 Americans die each flu season, according to the CDC.
So far this season, 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.
Based on data from the past two decades, during the years when H3N2 is the predominant flu strain, there are more deaths and hospitalizations, Bresee said.
It is not 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.
Flu is extremely unpredictable. Last winters flu season set a new record for the lowest and shortest peak of influenza-like illness. The season began late and was mild compared with most previous seasons.
The last time a regular flu season started this early was the winter of 2003-04, which proved to be one of the deadliest seasons in the past 35 years, with more than 48,000 deaths. The dominant type of flu back then was the same one seen this year.
But experts said there is a critical difference now: In 2003-04, the vaccine was poorly matched to the predominant flu strain.
Flu vaccines are designed to protect against the three influenza viruses that experts predict will be the most common during the upcoming season. Of the flu strains that are spreading this year, about 80 percent are the influenza A type, and almost all are the H3N2 strain, Bresee said. That matches well with this years flu vaccine, which includes the H3N2 strain.
Also, health officials said more vaccine is available now, and vaccination rates have risen for the general public and for key groups such as children, pregnant women and health-care workers.
About 112 million Americans had been vaccinated by the end of November, the CDC said. Manufacturers were expecting to produce about 135 million total doses this year. Flu vaccinations are recommended for everyone 6 months or older.
On Dec. 21, the Food and Drug Administration expanded the approved use of Tamiflu to treat children as young as 2 weeks old who have shown symptoms of flu. The drug was previously approved to treat adults and children 1 year and older.
The dose for children under 1 year old must be based on their exact weight.