MONDAY, Nov. 2 (HealthDay News) -- Results from ongoing clinical trials confirm that pregnant women need only one dose of the swine flu vaccine, while young children -- 6 months to 9 years of age -- need two doses, U.S. health officials said Monday.

These results are important because pregnant women and young children are especially at risk for complications from the H1N1 swine flu, Dr. Anthony Fauci, director of the U.S. National Institute of Allergy and Infectious Diseases, said during a press conference.

"I am pleased to be able to share some good news. Nearly all the pregnant women who received a single 15-microgram dose had a robust immune response," said Fauci, adding that the one-dose regimen produced a robust immune response in 92 percent of the women.

"This should be reassuring news to those women who have already received vaccine, and it is vital information for those pregnant women who have not yet been vaccinated," he said.

Also, further results from a trial involving 583 healthy children confirmed that kids 6 months to 9 years of age need two 15-microgram shots of the H1N1 flu vaccine, Fauci said.

"There was a sharp increase to the immune response to the vaccine after they received a second dose," he said. The second dose was given about 21 days after the first.

Among children 6 months to 35 months old, 100 percent had a robust immune response eight to 10 days after the second dose of the vaccine, as did 94 percent of the children 3 years to 9 years of age, Fauci said.

Earlier results from the trial had found that older children -- 10 to 17 years old -- needed only a single dose of the vaccine.

These are the same dose requirements that are recommended for the seasonal flu shot as well.

To date, the deaths of 114 children and 22 pregnant women have been positively linked to the swine flu, according to the U.S. Centers for Disease Control and Prevention.

Meanwhile, Dr. Anne Schuchat, director of CDC's National Center for Immunization and Respiratory Diseases, said Monday at the press conference that the shortage of H1N1 swine flu vaccine continues, because of variables with the egg-based production process.

"Expect continued challenges over the days ahead, but over time we expect that supply will start to increase and eventually catch up with the tremendous demand we are seeing now," she said. "It's getting better each day, but, unfortunately, it is not where we want it to be yet."

Schuchat said the available doses are being targeted to those most at risk, including pregnant women, children, young adults, parents or caretakers of infants, health-care workers, and older adults with chronic health conditions.

As of Friday, there were 26.6 million doses of vaccine in circulation, up from 16.1 million doses the week before, according to the CDC. First estimates by manufacturers had put the vaccine supply at 40 million doses by the end of October and 190 million by the end of the year.

The vaccine manufacturers have encountered several problems, which have slowed the production process. The main problem is that the virus grows more slowly than was predicted.

Over the last several years, the federal government has invested in newer, faster ways to make vaccines, Fauci said. "But it takes years to get where we want to be," he said.

The current technology requires growing the virus in eggs, Fauci said. "There are many fragilities about that, one of which is that the virus is variable in its growth -- if we are lucky it grows very well and we have a good yield on time," he said.

Also Monday, independent health advisers were to begin monitoring the safety of the H1N1 vaccine, an extra preventive measure the federal government promised in this year's unparalleled program to watch for possible side effects, the Associated Press reported.

Because the H1N1 swine flu vaccine is made the same way as the regular winter flu vaccine, officials don't expect any problems with the new inoculation.

Federal health officials haven't seen any problems so far, Dr. Bruce Gellin, head of the National Vaccine Program Office, told the AP.

On Sunday, ABC News reported that a study published earlier this year that found N95 respirators were better than surgical masks at preventing flu had been retracted. The retraction came on the last day of the Infectious Diseases Society of America annual meeting, in Philadelphia.

After a re-analysis of the study that was prompted by questions from reviewers, the findings were deemed no longer significant, said Holly Seale of the University of New South Wales in Sydney, Australia. The lead author of the study, Raina MacIntyre, also of the University of New South Wales, did not attend the Philadelphia meeting.

More information

For more on H1N1 swine flu, visit the U.S. Department of Health and Human Services.

SOURCES: Nov. 2, 2009, teleconference with Anthony Fauci, M.D., director, U.S. National Institute of Allergy and Infectious Diseases; Anne Schuchat, M.D., director, National Center for Immunization and Respiratory Diseases, U.S. Centers for Disease Control and Prevention; Associated Press; ABC News

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