The nation is having its earliest influenza season in nearly a decade and may see more severe illness than in recent years because of a circulating flu strain that has been particularly nasty in the past, federal health leaders said Monday.
The strain -- influenza A H3N2 -- has been associated with more serious illness and hospitalizations than other strains.
"It looks like it's shaping up to be a bad flu season, but only time will tell,"said Dr. Thomas Frieden, director of the national Centers for Disease Control and Prevention, in a conference call with reporters.
Five Southeastern states are reporting high levels of influenza-like illnesses, making this the earliest start to a regular flu season since 2003-04.
The nation also had an abnormally early season in 2009, but that was because of the appearance of the novel H1N1 virus, otherwise known as swine flu.
The flu season typically does not kick into high gear until January or later.
California is reporting only sporadic flu activity thus far, so there is still time for those who haven't been immunized to get a flu shot.
"We're seeing the storm clouds looming, but we have not seen flu activity here yet," said Dr. Randy Bergen, the clinical lead for Kaiser Permanente's flu vaccine program in Northern California.
Only about 1 percent of Kaiser's respiratory swab tests are coming back positive for the flu. Kaiser does not consider the flu season to have begun until positive tests reach 10 percent.
But because it takes about two weeks to develop immunity after a flu shot, Bergen advised people not to delay.
"It's only a matter of time before it makes it to California," he said.
The good news is that this year's vaccine appears to be a strong match for the circulating strains, including H3N2, which means it should provide optimal protection, Frieden said.
And plenty of vaccine is available. Nearly 123 million doses have been distributed out of about 135 million doses expected to be produced this season.
More than 112 million Americans have been immunized, said Dr. Melinda Wharton, acting director of the CDC's National Center for Immunization and Respiratory Diseases.
The CDC recommends that everyone 6 months and older be vaccinated.
"Vaccination is by far the best tool we have to protect ourselves," Frieden said.
Kaiser has immunized more than 1 million of its Northern California members, a 3 percent increase from last season, Bergen said.
Each year in the United States, as many as 200,000 people are hospitalized and 36,000 people die because of flu-related illnesses.
For the first time this year, Contra Costa and Santa Clara counties required health care workers who have direct patient contact to get a flu shot or wear a mask during the entire flu season.
Nationwide, vaccination rates among some health care workers have been high. Between 80 and 90 percent of pharmacists, doctors and nurses have been immunized, Frieden said. But he noted that vaccination rates need to increase among other health care workers, including those in nursing homes.
So if the flu season has not yet hit California, why are so many children suffering with runny noses, coughs and low-grade fevers?
Respiratory syncytial virus, or RSV, may be to blame. About 15 percent of Kaiser tests are coming back positive for RSV, which typically arrives about this time of year and strikes young children particularly hard, Bergen said.
RSV, a common cause of respiratory tract infection, tends to peak before the flu virus arrives in the Bay Area.
Sandy Kleffman covers health. Contact her at 510-293-2478. Follow her at Twitter.com/skleffman.
Contact your health care provider.
Many pharmacies offer shots for about $25 to $30.
Kaiser members can call 800-573-5811 or go to www.kp.org/flu.
Your local health department may offer free or low-cost shots.
Find a location near you by going to www.healthmap.org/flushot.