(CNN) The US Food and Drug Administration has given full approval to Pfizer's coronavirus vaccine for people age 16 and older. Approval for youths ages 12-15 is expected to follow soon.
"I don't think it'll be long before they extend it to 12 to 15 -- maybe within a few weeks to a month or so," said Dr. Bob Frenck, director of the Vaccine Research Center at Cincinnati Children's Hospital.
Parents are already clamoring to hear more about approval or authorization for children under 12, however. Studies looking at that are underway.
It appears that kids can get a much smaller dose of vaccine than adults and still get the same immune response, Frenck told CNN.
That's good news, because it means vaccine supply can be stretched further, Frenck said.
"We took a step back after we did the adolescents, and we looked at the dosing, because we thought that we may be able to use a lower dose and be able to get the same immune response," Frenck said.
It looks like children ages 5-12 get a strong immune response with 10 micrograms of vaccine antigen, Frenck said.
"So one third of the dose that we're giving adults, or even one third of the dose that was used in 12-year-olds and above, was just as immunogenic. We got just as good an immune response as the 30-microgram dose and there were less side effects," he said.
"So because of that, for the 5-12-year-old dosing we are looking at 10 micrograms, and then, in the younger kids, under 5, even going down further to 3 micrograms."
That might be confusing, but it simply means children have a stronger immune response, Frenck said. "It just really proves as far as that the kids' immune responses are good. They're very strong," he said.
"A lot of people are asking us: 'Does this mean you're giving us less of a vaccine?' I said, well, we're giving you less antigen, but their immune response is so good that they're making the same immune response -- so there's no need to give more vaccine," Frenck added.
"We're giving enough vaccine to be able to get the same immune response as we're seeing in people 25 years of age that are getting 30 micrograms."
More is not better, Frenck said -- the immune response hits a maximum and giving a higher dose doesn't boost it.
"We were able to decrease by a third, and still got the same immune response," he said.
As with adults, side effects are generally mild and do not last long, Frenck said.
"The side effects we're seeing in the kids are really identical to what we're seeing in adults," Frenck said. That includes a sore arm, fatigue, headache and fever in about 10% of children, he said.
Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said he was confident the trials would show good efficacy among younger children.
"I don't think there's going to be any question that this is going to be effective in the children at that younger age. I have no doubt about that," Fauci told CNN's Anderson Cooper Monday evening.
Dr. Amanda Dropic, a pediatrician in Florence, Kentucky, enrolled her four children in the trials for various ages at Cincinnati Children's.
"I talked to my kids about it. We all agreed that in order for everybody to get vaccinated, somebody has to be willing to step up and go first," she said in a video released by the hospital.
"We miss traveling. We miss vacations. We miss concerts. We miss sports activities. So hopefully as our kids are vaccinated and then other people get vaccinated, it'll really help," Dropic said.
"I am just really looking forward to hanging out with friends ... going to places without worrying about masks or where I can eat," said Dropic's son, Ben, now 16, who took part in the trial for Pfizer's vaccine in the 12-15-year-old age group.
"It is important to get the vaccine so you stop the spread of coronavirus and so the virus won't hurt any more people," said Ben's younger brother Eli, 10.
Frenck's team is starting vaccine trials now testing Moderna's Covid-19 vaccine in kids under 12. The hospital is due to enroll 75 children, he said -- 25 in each age group: 6-12, 2-6 and infants to age 2.
As with all the coronavirus vaccine trials, investigators like Frenck are speeding up the bureaucratic steps for submitting vaccine data to move the process along more quickly.
"Typically what happens is that you get a result from a Phase 1 (trial) and then you're showing it back to the company and saying, 'Okay, is this good enough that we're going to go to a Phase 2,' and then having to think about it. And then you same thing with Phase 2 to Phase 3. Here it just marched right along because the funding was already available," he said.
Often a study lasts four or five years, and the researchers gather all the data up at the end of that period of study and submit it to the FDA. "So you can imagine getting four or five years' worth of data all at one time -- that's a lot to try to process," he said.
"What happened here was that the FDA was being given packets of information in real time. As the companies got the information, it's being submitted to the FDA for them to review so when they got to a point in time of looking at the emergency use authorization, the FDA was already very familiar with the products and they didn't have to start from ground zero."
Moderna is also considering lower doses in younger children, Frenck said.
Pfizer says it will apply to the FDA for authorization to use its vaccines in children ages 5-11 by the end of September, once it sends all the data in.
Moderna, whose vaccine is authorized for people 18 and older, has filed with for EUA for children 12-17. It expects to have data ready on younger children later this year.
Johnson & Johnson is in "active discussions with regulatory authorities regarding our development plan and trial designs" for teens and children and expects to start trials in the fall.