The swine flu has also been particularly virulent among the Native American and Alaskan Native populations, Frieden said.
"The death rate is about four times higher for this group," he said. "This is most likely largely a reflection of environmental factors and underlying conditions -- like diabetes and asthma -- that are more common, and access to health care, rather than a genetic or racial/ethnic difference."
Frieden said that, as has been noted before, the rate of H1N1 flu infections has subsided in recent weeks, but it's impossible to predict what the winter and spring might bring. About half of the experts interviewed by the CDC think there will be many more cases, while the other half is taking the opposite view. "The truth is we don't know," he said.
Meanwhile, the supply of H1N1 vaccine continues to grow, Frieden said. There are now 85 million doses of vaccine available, up another 12 million doses from last week.
"This is a good window of opportunity to get vaccinated," he said. "We don't know what the future will hold in terms of H1N1 influenza."
The swine flu continues to produce mild infections in most people, with recovery taking about a week. But certain groups remain at risk for complications, including pregnant women, children and young adults, and people with chronic health problems, such as asthma, diabetes and heart disease.
Frieden also noted that cases of the regular, seasonal flu have begun to show up. Influenza B has already killed one child, he said.
So far this year, about as many people as last year have gotten a seasonal flu shot. With 109 million doses of seasonal flu vaccine available, most of the supply has been shipped. But, people are still experiencing shortages of this vaccine, Frieden said.
In related news, health officials in Vietnam said they have identified a cluster of swine flu cases resistant to the antivira
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