The number of older people hospitalized with the flu has risen sharply, prompting U.S. officials to take unusual steps to make more flu medicines available and to urge wider use of them as soon as symptoms appear.

The U.S. is about halfway through this flu season, and "it's shaping up to be a worse-than-average season" and a bad one for the elderly, said Dr. Thomas Frieden, director of the Centers for Disease Control and Prevention.

Carlos Maisonet, 73, reacts as Dr. Eva Berrios-Colon, injects him with flu vaccine in New York. About half of confirmed flu cases in the U.S. so far are in people 65 and older. (Bebeto Matthews/Associated Press)

It's not too late to get a flu shot, and "if you have symptoms, please stay home from work, keep your children home from school" and don't spread the virus, he said.

New figures from the CDC show widespread flu activity in all states but Tennessee and Hawaii. Some parts of the country are seeing an increase in flu activity "while overall activity is beginning to go down," Frieden said.

Flu activity is high in 30 states and New York City, up from 24 the previous week.

Nine more children or teens have died of the flu, bringing the nation's total this flu season to 29. That's close to the 34 pediatric deaths reported during all of the last flu season, although that one was unusually light. In a typical season, about 100 children die of the flu and officials said there is no way to know whether deaths this season will be higher or lower than usual.

The U.S. government doesn't keep a running tally of adult deaths from the flu, but estimates that it kills about 24,000 people most years.

So far, half of confirmed flu cases are in people 65 and older.

Lab-confirmed flu hospitalizations totaled 19 for every 100,000 in the population, but 82 per 100,000 among those 65 and older, "which is really quite a high rate," Frieden said.

"We expect to see both the number and the rates of both hospitalizations and deaths rise further in the next week or so as the flu epidemic progresses,"' so prompt treatment is key to preventing deaths, he said.

About 90 per cent of flu deaths are in the elderly; the very young and people with other health problems such as diabetes are also at higher risk. If you're worried about how sick you are and are in one of these risk groups, see a doctor, Frieden urged. One third to one half of people are not getting prompt treatment with antiviral medicines, he said.