The trials among children, which will ultimately be conducted at five universities in the United States, will allow researchers to determine effective and safe dosing of the vaccine, which has been designed to prevent a strain of influenza that has already claimed more than 1,000 lives worldwide.
"There was a lot of thought and consideration about the safest but most expeditious way to proceed, and we have completed enrollment," said Dr. Karen Kotloff, lead investigator of H1N1 studies conducted at the University of Maryland School of Medicine, which is leading the trials. "This is a vaccine that is made in exactly the same way as the standard, licensed flu vaccine."
Roughly 600 children are enrolled in the National Institutes of Health's trials, she said. They are evenly divided into three age groups: 6 to 35 months, 3 to 9 years, and 10 to 17 years.
Children will receive two doses of vaccine, with half receiving 15 micrograms of antigens -- just as they would for each of the three strains in seasonal flu vaccine -- while others will receive30 micrograms to see if a higher dose is needed to protect against swine flu.
Younger children will undergo three blood draws to test vaccine effectiveness while children above the age of 10 will undergo five -- similar to adults -- a concession to the younger children's dislike of having blood taken.
"We try to spare children the anxiety and discomfort associated with blood-drawing," Kotloff said.
For the most part, children's trials are similar to the adult version, but with a few notable differences.
"The difference is we have to get consent from both the parents and the child," said Dr. Janet Englund, a pediatrician with Children's Hospital, Seattle, who is running one of the five branches of the study, explaining that any child 7 or older must give their own consent to participate in the trial. She said that about 2 percent of children do refuse to participate.
While some concerns have been raised about the speed of clinical trials in children for the flu vaccine, doctors cited both the concern of having vaccine available in time for flu season and the history of medications needed for adults and children as reasons for the child trial following so soon after the start of the adult one, which started on Aug. 7.
"The history of doing clinical trials in kids is an evolving one. We are now in the stage in our evolution where kids' trials start sooner than they used to," said Dr. Harley Rotbart, professor and vice chairman of pediatrics and microbiology at the University of Colorado Health Sciences Center at Denver and author of "Germ Proof Your Kids," who is not involved in the NIH's clinical trials.
He said that testing on children is often done quickly after testing in adults because pediatricians used to have difficulty knowing how to dose medications in children.
"When a pharmaceutical company would get approval in adults, they would never do [clinical trials] in children," he said. "We ended up treating children as mini-adults."
Side effects, said Rotbart, could present an issue.
"One issue is dosing, but the second issue is that adults and children have different rates of and types of side effects from vaccines," he said.