While levels of flu remain high throughout parts of the United States, some areas are reporting declines, government health officials reported this weekend.
"We have seen a national peak in influenza, but we are still seeing some increases in activity, specifically on the West Coast, and the Northeast and New England," said Dr. Lyn Finelli, chief of surveillance and outbreak response in the influenza division of the U.S. Centres for Disease Control and Prevention.
"We expect we will see high flu activity for several more weeks," she added.
However, at the end of January, 10 states reported minimal flu activity. They were Alaska, Florida, Illinois, Indiana, Iowa, Michigan, New Hampshire, Ohio, Oregon and Wisconsin.
Since the start of the current flu season, the predominant type of flu has been an H3N2 strain that is not a good match to this year's vaccine. The majority of H3N2-related infections diagnosed so far – 75 percent – are different from the strain in the vaccine, Finelli said.
The reason: The circulating H3N2 strain mutated after scientists settled last year on the makeup of this season's flu shot.
This year's flu season continues to hit children and the elderly hardest. By 31 January, 69 children had died from complications of flu.
In an average year, children's deaths vary from as few as 30 to as many as 170 or more, CDC officials said.
Read: What is flu?
As the season continues, Finelli expects to see a surge of other flu strains. "About this time of year, in February and March, we see an increase in influenza B," she said.
That could be good news on the vaccine front. Right now, the flu vaccine is only about 23 percent effective, because of the mutated H3N2 strain. But as other strains become more widespread, the vaccine's effectiveness should increase, she said.
Most years, flu vaccine effectiveness ranges from 10 percent to 60 percent, according to the CDC.
More common among the unvaccinated
Twenty-three percent effectiveness means there's some benefit – a little less flu among vaccinated people. Typically, flu is more common among the unvaccinated, but this year there's been a lot of flu both in people who are vaccinated and those who aren't, CDC officials said.
Vaccine effectiveness is also related to the health of those getting the shot. Flu vaccine usually works best in young, healthy people, and is less effective in those 65 and older, the CDC said.
So far, this year's shot has been most effective – 26 percent – for children 6 months old through 17 years. Older people have been getting less benefit – 12 percent effectiveness for those 18 to 49 years and 14 percent effectiveness for those 50 and older, the CDC says.
Read: Genes may affect response to flu shot
The CDC recommends that everyone 6 months and older get vaccinated. Vaccination can prevent some infections and reduce severe disease that can lead to hospitalisation and death, the agency says.
Other ways to treat and prevent flu from spreading include early treatment with antiviral drugs such as Tamiflu and Relenza, and washing hands frequently and covering your mouth when coughing or sneezing.
Early treatment is important
Early treatment with antiviral drugs is especially important for children 2 years and under and adults 65 and older, Finelli said.
Others for whom these drugs are essential are people with diabetes, heart disease or breathing problems, she said.
Read: Nearly half of Americans think flu shot can make you sick
By 31 January, all areas of the country reported flu activity at or above baseline levels, the CDC reported. Twenty-six states and Puerto Rico experienced high activity.
Eight states and New York City experienced moderate activity. Another six states reported low activity.
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