Most healthy pregnant women and children ages 10 to 17 can be protected against the novel H1N1 flu with a single dose of vaccine, the National Institute of Allergy and Infectious Diseases said Monday.
However, healthy children ages 6 months to 9 years will require two doses several weeks apart for optimum protection.
These are the findings of clinical trials conducted with volunteers between Sept. 9 and mid-October. They follow earlier preliminary data of trials conducted at only eight to 10 weeks whose findings were similar.
Blood analysis samples taken at 21 days after vaccination showed a 15-microgram dose was likely to work in 92 percent of pregnant women - considered to be among those most vulnerable to the current flu strain. A single 30-microgram dose produced a robust response in 96 percent of the women tested.
An additional dose offers no real advantage, Dr. Anthony S. Fauci, institute director, said at the news conference in Washington. “This should be reassuring news to those women who have received the vaccine and vital information for those who have not been.”
Among very young children, the immune response showed “a sharp increase” with a second dose. But parents should not delay getting their children a first dose, because even if a second one is not available within the recommended four weeks, “you still get a booster effect,” he said.
Dr. Fauci and Dr. Bruce Gellin, director of the National Vaccine Program Office, sought to reassure the public about the safety of the new vaccines. A group of independent specialists has been appointed to monitor data gathered by government offices.
“With regard to adverse events, there have been no red flags about serious events,” Dr. Fauci said.
Regular telephone surveys are being conducted to determine what portion of the population is getting a seasonal vaccine as well as the H1N1 flu shot.
“States also are tracking information on doses being administered,” said Dr. Anne Schuchat, director of the National Center for Immunization and Respiratory Diseases at the Atlanta-based Centers for Disease Control and Prevention. “We know half of the vaccine administered so far has gone to children under 18.”
On Friday, Dr. Thomas Frieden, CDC director, said 114 U.S. children and teenagers have died since the swine flu outbreak in April, two-thirds of whom had underlying medical conditions.
Also on Friday, federal health officials said they would release 300,000 doses of the liquid form of the antiviral Tamiflu to make sure enough of the medicine is available to sick children.
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