FRIDAY, Sept. 11, 2009 (HealthDay News) -- U.S. health officials said Friday that additional trials of the H1N1 swine flu vaccine continue to find that a single dose produces a strong immune response in healthy adults.
The findings confirm study results released Thursday out of Australia and Britain that found that a single dose of the vaccine creates enough antibodies to protect against the virus within about 10 days.
Despite the encouraging news about the vaccine, the officials noted that flu activity is unusually high for this time of the year, and virtually all of the infections are coming from the H1N1 swine flu strain.
The first 45 million doses of the H1N1 vaccine aren't expected until mid-October. And results of trials of the vaccine in young children and pregnant women -- two of the groups high on the vaccine priority list -- won't be available for several more weeks, officials said.
"We are encouraged by the data we've seen both in other countries and here in the United States," Kathleen Sebelius, secretary of the U.S. Department of Health and Human Services, said during an afternoon press conference.
"It appears we will need only one dose for most healthy adults and the vaccine we are producing is working extremely well," she said. "That is critically important news."
It had been thought that two shots would be needed to provide full immunity to the virus. A one-dose regimen would greatly expand the supply of vaccine and hasten individual immunity.
In the trial results released Friday, 96 percent of healthy adults between the ages of 18 and 64 had a strong immune response to the 15-microgram dose of the vaccine produced by drug maker Sanofi Pasteur. The response rate to the 15-microgram vaccine made by CSL Limited was 80 percent, said the officials, who downplayed the difference in the response rates.
Sebelius also said the 15-microgram vaccine acts faster than had been anticipated, so people will be protected sooner after getting their shot. "It appears that most folks have a robust immune response in eight to 10 days, which is very positive news," she said. "The vaccine that we have purchased will go further and help us cover more people."
The United States has ordered 195 million doses of the H1N1 swine flu vaccine from drug makers.
Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said the vaccine trials involving pregnant women are just starting and results are not expected until late October.
"Children are lagging behind the adult trial so we will get some preliminary data in about two weeks on the children," he added.
Still to be determined is whether two shots will be needed for pregnant women and children, Fauci said.
Dr. Anne Schuchat, director of the National Center for Immunization and Respiratory Diseases, said flu activity is increasing around the country and the H1N1 pandemic flu makes up virtually all of the circulating virus.
"Ninety-eight percent of the viruses that are circulating right now are this new H1N1," she said. "The levels of flu activity we are seeing this September are extremely unusual for this time of year."
Schuchat noted that hospital visits for flu right now are as high as they were at the peak of last year's regular flu season. "This increase in flu activity is mainly in children and young adults," she said.
The good news, officials said, is that the H1N1 swine flu continues to produce relatively mild illness in most people and recovery time is fairly quick.
People under 60 years of age are considered at higher risk of infection from the swine flu because, unlike older adults, they haven't been exposed to the H1N1 virus.
With so much flu activity already under way, and the earliest vaccine deliveries not expected for another month, there are steps people can take to protect themselves.
Those steps include frequent hand washing, covering your cough and staying home if you are sick.
Sebelius also urged people not to forget about seasonal flu, which could start circulating in the weeks to come. She encouraged people to get their seasonal flu shot, which is available now.
Unlike swine flu, the traditional seasonal flu tends to strike harder at older adults.
For more on H1N1 flu, visit the Flu.gov.