(CNN) With more than 44 million people fully vaccinated against Covid-19 in the United States, many adults are hopeful that a more normal life is on the horizon. Now families are wondering when vaccines will be available for teens and children.
Covid-19 vaccines currently authorized in the United States are only available for adults, except Pfizer/BioNTech's vaccine, which is authorized for people ages 16 and older.
While there's a chance that a vaccine will be available to high school and middle school-age children by this fall, younger children may still be months away from vaccination when the upcoming school year begins. Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, has said younger children may have to wait until the first quarter of 2022.
Trials are getting under way, though. This week, the first children received a shot in Pfizer/BioNTech's Phase 1 trial of children under the age of 12. The company aims to enroll 4,644 children between the ages of 6 months and 11 years in Phase 1 and 2/3 and expects results by the end of 2021.
Last week, the first children were vaccinated in Moderna's Phase 2/3 KidCOVE pediatric trial, which includes children ages 6 months to 11 years.
Dr. Buddy Creech, director of Vanderbilt University's Vaccine Research Program and an investigator in Moderna's pediatric trials, estimates a Covid-19 vaccine won't be available to children 11 and younger until November or December, at the earliest.
Pfizer/BioNTech and Moderna have been testing their vaccines in youth as young as 12, and experts are feeling confident that the results will be ready in time to get kids 12 and up vaccinated for the upcoming school year. Pfizer evaluated its vaccine in 2,259 children between 12 and 15 before deciding it looked safe enough to move into younger children, the company told CNN, adding that it will likely share the safety and efficacy data soon.
Creech said vaccines could be available for high-risk kids 12 and older by July or August.
Johnson & Johnson has announced plans to begin testing its vaccine in youths ages 12 to 18, and J&J CEO Alex Gorsky said this month that the company will likely have a vaccine available for children under 18 by September. In February, the University of Oxford announced it would begin testing AstraZeneca's vaccine in kids and teens ages 6 to 17. Novavax said it expects pediatric trials of its vaccine to kick off shortly.
But each vaccine needs to be carefully tested in pediatric populations until enough data is generated for the US Food and Drug Administration to evaluate whether it is safe and effective.
Parents and teachers should be vaccinated by this fall, but many kids, especially those under the age of 12, will likely not be.
Children are much less likely to get seriously ill or die from Covid-19 than adults, and there is increasing evidence that with the right precautions, the risk of in-school virus transmission is low.
"Children's hospitals have not been full because of this pandemic," said Creech. "The pandemic raged in the United States -- more than any other country -- and yet our children's hospitals were typically being used for the overflow from adult hospitals."
Most health experts and authorities, including the US Centers for Disease Control and Prevention, don't list vaccinating children as a prerequisite for a return to in-person learning, but it will add a degree of protection for students, school staff and their families.
Pediatric Covid-19 vaccine trials will aim to determine whether vaccines can protect kids from becoming sick if they are exposed to the virus. Researchers will test the vaccines in teens first and work their way down to younger age groups, which may need different dosages.
"We start with low doses and move up in the dosage until we find that Goldilocks moment, where we give them just enough of the vaccine to get the right immune response but without a high amount of side effects," Creech said.
All participants in the initial part of Moderna's KidCOVE study will receive two 25, 50 or 100 microgram doses of the vaccine, so researchers can determine the appropriate dosing. Then the trial will expand to include participants who are given a placebo, so the safety and efficacy of the vaccine can be studied.
Pfizer's trial in children under 12 will test 10 to 30 microgram doses of the vaccine. At first, two-thirds of the children will receive the vaccine and the others will receive a placebo. At a six-month follow up, those who received the placebo will be eligible for the vaccine.
Dr. Steve Plimpton, an OB-GYN and investigator for the KidCOVE study in Phoenix, Arizona, said the 14-month study will include planned pauses, check-ups and blood draws.
Researchers hope to build off the knowledge gained in the adult trials.
"What we're hoping for, and I think what we're close to, is being able to define a number of antibodies in the bloodstream that are a correlate of the protection that we saw in those big Phase 3 trials of 30 to 40 thousand people," said Creech.
Researchers will then look for that level of antibodies in pediatric participants to know that the vaccine is providing protection.
"That way we don't have to do studies of 30,000 children, we can do studies of five or ten thousand children instead," Creech said.
"Children are not just little adults," Creech said. "They have immune systems that look a whole lot like adults, but they have a different level of training, they've seen fewer viruses and they have fewer health problems."
While it's not unusual for a 40-year-old to experience a fever and sore arm after getting vaccinated, those side effects may be more difficult for a 9-month-old to tolerate.
"We want to be really thoughtful so that as we launch vaccine campaigns in children, we can give pediatricians -- but most importantly, parents -- a full expectation of what they might see over the day or two following vaccine," Creech said.
Dr. Robert Frenck, director of the Vaccine Research Center at Cincinnati Children's Hospital and investigator for the Pfizer trial at the hospital, reviews "symptom diaries" that participants are asked to keep.
"The kids -- if they're having symptoms -- are having headaches, they're having fatigue. They may have some muscle ache, but other than that, really not much," said Frenck. "Most symptoms are going away in a day or two. There's a number of people that have almost nothing."
Some children who contracted Covid-19 experienced MIS-C, or multisystem inflammatory syndrome in children, which is rare but can cause severe illness in some.
"We're going to be watching that with particular interest to make sure that we aren't seeing it in association with the vaccine, or in association with the vaccine plus an infection that they might develop months down the road," said Creech. "There's no reason to think that that's going to happen due to the vaccine alone, but we're going to be looking for it."
Participants will also be monitored closely for rashes, fever, fatigue or other health issues.
Covid-19 vaccine clinical trials are overseen by a Data and Safety Monitoring Board (DSMB), comprised of independent experts who have access to trial data and can recommend studies be halted if there are safety concerns.
Dr. Kathryn Edwards is a scientific director at Vanderbilt University's Vaccine Research Program and a member of the DSMB for a Covid-19 vaccine that will be tested in children.
"If children get sick, they'll be seen by the investigators to see whether there was any possibility that the illness is related to the vaccine," said Edwards. "There will be meticulous attention to safety concerns."
Plimpton said he has seen an enthusiastic response to the call for participants for Moderna's KidCOVE study, which aims to enroll 6,750 participants in the US and Canada.
"It's amazing how much the parents are coming out and are willing to try to help us get this cleared for their kids," said Plimpton. "I told Moderna that we could probably get all 6,750 patients here in Phoenix -- and they have 75 sites in the United States and Canada."
Plimpton noted that the trial does not have specific demographic requirements, but the response has been diverse and trial sites are spread out across the nation to include a broad range of participants.
"For the most part, we're getting everybody," he said. "It's happening because all parents want to protect their kids."
Rachel Guthrie, a labor and delivery nurse in Phoenix, Arizona, enrolled her 3-year-old son and 2-year-old daughter in the Moderna trial. She said she wants to protect her children from any exposure she encounters and wants her son to have some degree of protection at his in-person preschool. They're set to receive their first shots this week.
"I jumped at the opportunity, because I want my children to have that protection," she said. "To get the approval of this vaccination for kids, someone has to be willing to step forward."
Researchers are hopeful that kids won't be the only ones who benefit from the trials.
"We also want the study to give other demographic groups peace of mind that they can go get the vaccine. 'Hey, this 6-month-old baby got the vaccine -- why am I, as a 25-year-old, not willing to do it?'" said Plimpton.