While local effects of the injection might be shrugged off in adults, they would be taken more seriously in children.
"Kids are not just little adults, and all the questions that we asked when we do adult trials have to be asked again, because kids are a different species," Rotbart said.
Kotloff noted that those concerns present themselves in swine flu vaccines, hence the separation by age group.
"There's different information that you get from each age group," she explained, although she noted that is most obvious with the oldest patients. "It does seem that people over about age 50 have some immunity to this H1N1 swine flu. Children have little or no immunity."
She noted that this might affect both the number of shots and dosing to provoke an immune response.
"The amount of vaccine for immune status may differ by age group," Kotloff said.
While some parents might worry about enrolling their children in a clinical trial, doctors said those concerns could be assuaged.
For one thing, noted Dr. Kathryn Edwards, the pediatrician running Vanderbilt's branch of the clinical trial for swine flu vaccine, no one in the study would be receiving a placebo.
"Everybody wants to get some protection; they don't really want to go through this process and get nothing," she said.
Additionally, she noted that all the adults vaccinated for swine flu at Vanderbilt have been followed up with and no adverse events have been reported.
"The other thing that gives us a lot of confidence is this vaccine is made the same way as the flu vaccine we make every year," she said.
Doctors also noted that they would have their own children participate, and many of them do.
"At this one site, of the first 50 people who signed up, most of them were actually the children of medical professionals," Kotloff said.
Englund noted that her own children, while now too old to participate in children's trials, had done so in the past.
"As someone who's been doing this for 30 years, I would never give a vaccine if I wouldn't give it to my own children or grandchildren," Edwards said. "There is a very sophisticated and integrated data safety and monitoring committee that includes experts in pediatric and adult medicine."
She said that one person who had gotten the adult vaccine came in complaining of muscle aches, but it was ultimately determined that the person got the aches from pulling weeds, not the vaccine.
"He couldn't move, but obviously he had another reason or another explanation," Edwards said. "The assessment of adverse events is taken very seriously."
Edwards also noted that safety was determined separately from efficacy.
"That data safety and monitoring team does not include any investigators," she said. "It is a totally independent group."
Ultimately, Edwards said, she believes that the trial for the vaccine would likely be not only safe, but effective.
"I spent about two days going through old freezers here to find blood from children who were in the 1976 vaccine trial," she said, referring to the last outbreak of swine flu in the United States.
She had those tested, and they were found to have responded to the vaccine. She said she sees this vaccine producing an immune response, unlike the avian flu vaccine.
"I think that from that experience, we would suggest that two doses likely will work," she said.