H1N1 Deaths Among Youths Rise as Epidemic Spreads

So far, states and cities have ordered 3.7 million doses of the 6.8 million that have become available, and the first doses were administered this week. Some doctors and clinics are reporting being flooded with requests for the vaccine. But several national surveys have found that only about 40 percent of Americans are sure they will get it, with those who are reluctant citing doubts about the severity of the virus and concerns about side effects.

The vaccine campaign is also fueling anti-government sentiments and false rumors that the vaccine is mandatory. Although New York state and some individual hospitals and private health chains are requiring their employees to get vaccinated this year for the first time, the vaccine remains voluntary for most people.

"Lots of rumors out there, and we're trying to address them," Schuchat said.

Additional data from federal studies testing the vaccine have found no evidence of any unusual risks and have confirmed preliminary indications that the vaccine is effective for most adults with one standard dose.

At least 37 states are reporting widespread flu activity, up from 27 a week ago. While the number of cases appears to be decreasing in some places, it is increasing in others and could rise again in areas where cases are dropping, Schuchat said. New York and some other cities that experienced large outbreaks in the spring are reporting fewer cases than expected, but Schuchat warned that could change at any time.

"It's hard to know how many waves we're going to have into the fall, winter and spring," she said. "We still think the vast majority of people in a given community are vulnerable or susceptible to this virus."

Although the virus causes mild illness for most people, some people become seriously ill, requiring intensive care to try to save them.

"Unfortunately, we do expect more illness, including more hospitalizations and deaths, to be occurring in the weeks ahead," she said.

Schuchat also encouraged people to get the seasonal flu vaccine. Some areas are experiencing shortages of seasonal flu vaccine, in part because manufacturers are juggling production of both vaccines. New data from another federal study aimed at determining whether people can get both vaccines at the same time found that was no problem.