Children under 9 years of age may need two doses of the vaccine to be protected, Schuchat noted.
Many Americans may be heeding the CDC's vaccination advice this year. "We are encouraged by the number of people who have already received the flu vaccine," Schuchat said.
According to an agency survey, as of mid-November about a third of Americans had already been immunized. Another 15 percent said they planned to get vaccinated and 25 percent said they probably would get vaccinated, Schuchat said. That's about the same as last year, she added.
The highest proportion of people who have been vaccinated are those 65 and older, with about 64 percent of vaccinations occurring among seniors, according to the survey.
In other CDC surveys, the agency found that 56 percent of health-care workers reported having gotten their flu shot. Another 7 percent plan to get vaccinated, Schuchat said.
Among pregnant women -- a group hit especially hard by H1N1 last flu season -- 45 percent said they had already been vaccinated and another 4 percent said they planned on getting the shot.
This year the vaccine is available at record levels, with more than 160 million doses already distributed, Schuchat said.
Speaking at the news conference, Dr. Howard Koh, assistant secretary for health in the U.S. Department of Health and Human Services, said that "flu activity is increasing across the country. If you've been thinking about getting vaccinated for influenza, now is a good time to do so."
The flu is unpredictable and potentially deadly, so everyone should get a flu shot, he added.
Koh noted that under the new Patient Protection and Affordable Care Act, all new health insurance plans will cover flu shots, with no co-pays.
According to CDC estimates, approximately 5 percent to 20 percent of Americans get the flu each year, and
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