Australian vaccine maker CSL said on Monday its pandemic H1N1 swine flu vaccine delivered a strong immune response after just one dose in children as young as 6 months.
Global health authorities recommend children get two swine flu shots for full protection, but the CSL vaccine showed strong response with just one shot.
"This is great news that kids, including the very youngest kids, responded with a single dose. It really is as good as we would have hoped," said Dr. Anthony Fiore of the U.S. Centers for Disease Control and Prevention, who wrote a commentary that accompanied the study in the Journal of the American Medical Association.
The findings suggest a single shot of the vaccine could protect infants and children, a group that has been especially vulnerable to pandemic H1N1 influenza.
In the study, a single 15-microgram dose produced protective antibody levels in 92 percent of children aged 6 to 36 months, and 92.9 percent in children aged 3 to 9.
After a second dose, 100 percent of children in both age groups were protected. No serious safety concerns were reported with the vaccine.
"The key finding is really that one dose of the swine flu vaccine appears to be highly effective in children as young as six months of age," Dr. Michael Greenberg, director of vaccines clinical development with CSL, said in a telephone interview.
"While we've seen similar responses in adults, the fact that we were able to achieve protective antibodies in the majority of children even after one dose of the vaccine is what makes these findings unique."
Currently, all H1N1 vaccines in the United States for children 3 and over are given in a 15 microgram dose, while children 6 months to three years get a 7.5 microgram dose of vaccine, Fiore said in a telephone interview.
The CSL study also tested the higher 15-microgram dose in the youngest children, and found no significant side effects.
"They were testing a double dose of vaccine in those younger kids -- more than is currently approved," Fiore said.
Fiore said it is not clear exactly why children in the study did so well on a single dose of the vaccine. He said it may be that some had unknowingly been exposed to swine flu and their immune systems were already primed, or it may be the way they were tested in the lab. Or, he said, it may be that the CSL vaccine simply produces a better immune response.
Fiore said the findings do not suggest that all swine flu vaccines approved for children require only dose. Tests of other vaccines show children need two doses for good protection.
"It's one vaccine, one study, one year, and it's in the context of fairly long experience with young children who have never before been vaccinated needing two doses," he said.
The CDC estimates that swine flu has killed 10,000 Americans, including 1,100 children, and put 200,000 into the hospital since it emerged in March.
The U.S. government has been struggling to vaccinate 160 million Americans considered in most need of H1N1 vaccination but had 100 million doses of H1N1 vaccine as of last week. CSL is contracted to provide 36 million doses of vaccine, and Greenberg said so far the company has delivered everything the government has asked for.