Clinical trials of the vaccine in adults began recently, and so far, there have been "no red flags" of safety concerns, Anthony Fauci, MD, director of the National Institute of Allergy and Infectious Diseases, said today in a news conference.
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Based on those early reports, clinical trials have begun in children ages 6 months to 17 years, Fauci said.
Results of the clinical trials are still several weeks away, and more trials will begin in September to test the vaccine in pregnant women, who are a high-risk group for swine flu complications.
At today's news conference, CDC officials also reported that nearly 8,000 hospitalizations and 522 deaths in the U.S. have been confirmed as caused by the H1N1 swine flu virus.
Flu activity is at a low level in the U.S. but flu is widespread in two states: Alaska and Maine. Most of the flu in the U.S. is swine flu right now, as the regular flu season hasn't begun yet.
Swine flu "continues to disproportionately affect younger persons," said Jay Butler, MD, director of the CDC's H1N1 task force. Butler noted that in the U.S., 75% of swine flu hospitalizations and 60% of swine flu deaths have been in people younger than 49.
In other swine flu news, press reports quoted a World Health Organization official as saying that there could be an "explosion" of swine flu cases.
Asked about that in today's press call, Butler said an "explosion" of cases would be one of the worst-case scenarios that health officials are preparing for, but that it's not certain to happen.
"Whether or not it will be an 'explosion,' we really can't say," said Butler, stressing the unpredictability of flu viruses.
Butler and Fauci noted that more cases are likely in the fall and winter, as children head back to school and as the weather turns colder. "Hopefully it's not going to be bad but we'll be prepared for it," Fauci said.