As , doctors say America's chances of winding down the COVID-19 pandemic in the U.S. will largely .
Now, toddlers and babies as young as 6 months old are testing COVID-19 vaccines to help make sure they're safe for other young children. If the pediatric trials go well, children under 12 might be eligible to get vaccinated this fall or winter.
For many parents, the decision to volunteer their kids was easy.
One family knows the anguish of suddenly losing a healthy child to unexpected illness and doesn't want any other family to endure the same.
Other parents want their children to go back to school and play with friends safely -- without masks and without worrying about new coronavirus strains or complications such as .
And one family is so passionate about helping protect kids, they've enrolled all three children -- ages 6, 3, and 14 months -- in a COVID-19 vaccine trial.
Here's what parents who have stepped up to volunteer their children want other families to know:
'You don't want to be that statistic'
Rebecca and Michael Calloway never imagined they would lose their healthy, energetic toddler to an unexpected illness.
Shortly after Thanksgiving, 3-year-old Ailish became severely sick and was hospitalized with swelling in her brain. She died just a few days later.
"It turned out that she had undiagnosed type 1 diabetes," Rebecca Calloway said. Type 1 diabetes is not preventable, the says.
"We lost our daughter to something we couldn't control," Calloway said.
But COVID-19 "is something we can control. (Vaccines) have ."
"We can be part of showing people that yes, this is safe," the mother from rural Maryland said.
"This is going to keep your children safe. It's going to keep (those) who cannot be vaccinated safe. We want to be part of that."
So her 7-year-old daughter Georgia is testing the Moderna COVID-19 vaccine.
Their youngest child, 2-year-old Lochlan, is already a vaccine trial veteran. When he was 2 months old, he started participating in a meningitis vaccine trial.
"They want to work towards improving it for younger children because meningitis is something that young children are still getting and dying from," Calloway said.
While childhood deaths from meningitis, type 1 diabetes and COVID-19 are rare, . And when it happens to your family, Calloway said, the grief is overwhelming.
"You don't want to be that statistic," she said. "I would never, ever want someone to go through the pain of losing a child. It's devastating beyond anything that you can imagine."
Even before Ailish's death, the Calloways planned to support vaccine trials because their relatives suffered consequences from not being vaccinated in the past.
"My family and my husband's family have a history with fallout from not having vaccines," Calloway said.
Michael's grand-aunt died from . His father nearly died from . Rebecca's grandmother had and contracted while she was pregnant with Rebecca's uncle, who was born completely deaf and with brain and heart problems.
"We've seen the effects of what can happen without vaccines. Those are very real to us in our family," Rebecca Calloway said.
Even at age 3, Ailish also had a passion for helping others. She started telling everyone she wanted to be a doctor.
Calloway said Ailish would have been so proud of her sister Georgia for testing the COVID-19 vaccine.
"Georgia was her hero," their mother said.
Without vaccinating kids, it's 'going to be impossible to get to herd immunity'
Dr. CJ Bui is a pediatric neurosurgeon. But when COVID-19 started overwhelming hospitals, he and other doctors from different specialties volunteered to help treat COVID-19 patients.
"Seeing how bad it can be for adults, (even) young adults" was sobering, the Louisiana doctor said. "I've seen a healthy 30-something-year-old die a miserable death."
Now, as spread among unvaccinated people, Bui and his wife have enrolled all three of their children in a Pfizer COVID-19 vaccine trial.
"We both saw how terribly COVID affected patients," said Bui's wife, neurosurgeon Dr. Erin Biro. "We felt strongly about participating in the research -- obviously for the opportunity to have our kids vaccinated (and) to continue to move the needle forward in the battle against COVID."
Their 6-year-old daughter Ellie got her first shot June 8. Her younger brother Christian, 3, and baby sister Sloane, 14 months, received their first injections June 21.
This Phase 2/3 of the Pfizer study is double-blinded, so the family doesn't know whether each child received a dose of COVID-19 vaccine or a placebo. Six months after the second injections, the study will be "unblinded," and those who got a placebo will be able to get the real vaccine.
None of three Bui children had side effects after their injections, their parents said.
Before volunteering their children, Bui and Biro evaluated the risks and benefits -- from the perspectives of both doctors and parents.
"If you really look at the data, the risk is exponentially lower from this vaccine than a lot of common medications. So that played a role," Bui said.
Another reason was the need to suppress coronavirus before it mutates into or .
Bui said without widespread child vaccination, "It's really going to be impossible to get " -- or the point at which enough people are protected against a virus to suppress its spread.
As more variants develop and spread among unvaccinated people, the bar for reaching herd immunity may become higher.
"We're potentially one variant away from removing all this progress," he said.
Bui's also concerned about MIS-C, or -- a that can happen in children weeks after a coronavirus infection.
The doctors also share a desire echoed by many parents: They want children to learn in classrooms, "full time and back to school safely," Biro said.
"And safely, for us, meant vaccination."
How children's COVID-19 vaccine trials work
The only COVID-19 vaccine available to minors in the US is the Pfizer vaccine, which is authorized for ages 12 and up. (Moderna has .)
Both Pfizer and Moderna have started COVID-19 vaccine trials in children between ages 6 months and 11 years.
In the first part of , all participants get vaccinated at varying levels, with no placebos. And families know what dose their kids are getting.
Children ages 2 to 11 are given one of two possible dose levels -- 50 micrograms or 100 micrograms per dose. (Each .) Participants ages 6 months up to 2 years may get one of three dose levels -- 25, 50 or 100 micrograms.
"An interim analysis will be conducted to determine which dose will be used in Part 2, the placebo-controlled expansion portion of the study," said.
Some may be surprised babies could test adult doses. But parents don't need to worry about a so-called overdose, said pediatrician Dr. James Campbell, lead investigator of the Moderna children's vaccine study at the University of Maryland School of Medicine.
"These are very, very small amounts," he told CNN. "So when you're talking half or double of a very small amount, it's still a very small amount. You cannot overdose on vaccine doses."
What might happen is higher doses may lead to more side effects. That's what investigators are trying to determine, Campbell said.
"Could it be that 100 micrograms leads to 10 per cent of people having fever, and 50 micrograms leads to 5 per cent having fever? ... That's what we're looking for," he said.
Scientists are trying to see which doses yield the best combination of high efficacy and minimal side effects.
Of course, 6-month-olds can't describe any side effects they might get. So how would parents know if their young child is having side effects?
"It's the same as any other child who gets ill -- they get fussy," said Dr. Julia Garcia-Diaz, a lead investigator for Pfizer's pediatric vaccine study at New Orleans' Ochsner Hospital for Children.
"They're not eating the same, or they're fussy and they just cry. Parents are attuned to how their child behaves," she told CNN.
Any adverse side effects from vaccines almost always "show up within the first two weeks, and certainly by the first two months" after vaccination, Dr. Ashish Jha, dean of the Brown University School of Public Health, .
Garcia-Diaz agreed with that time frame.
"After that, your body has made the antibodies. It has done what it is supposed to do," she said. "So most likely things that are outside that window are not related."
While some families are hesitant to vaccinate their children, many have been eager to participate in the vaccine trials, Campbell and Garcia-Diaz said.
"There has been a great deal of interest," said Garcia-Diaz, director of clinical infectious diseases research at Ochsner Health.
"The parents had been calling us for weeks on end trying to find out when the trial starts."
Pfizer's trial for young children started in March, and it expects to ask the U.S. Food and Drug Administration for emergency use authorization for ages 2 to 11 years in September, the company said.
Moderna said if trials go well, its vaccine may be available for children under 12 years old this winter or in early 2022.
A 9-year-old feels like he's helping 'save the world'
Dr. Charles Mugera has seen patients rapidly deteriorate with COVID-19.
"I was admitting patients every day, sending them to the ICU -- some of them dying on the floor," said Mugera, an internist in Maryland. "Going to work every day was scary, not only for what's going to happen to patients but what's going to happen to us" health care workers.
"This vaccine has just changed the game entirely."
He's been monitoring the data and knows .
"We have seen not only , but transmissibility has gone down because we're vaccinated don't transmit the disease," Mugera said.
"So it becomes very clear that for this pandemic to end, we have to not only protect ourselves from severe disease but (also) get the children vaccinated. Because even though the children have not been perceived as being at risk for death and severe disease, they transmit it."
His wife, Dr. Kabuiya Ruth Mugera, is a pediatrician who also believes children need to be vaccinated against COVID-19.
So they asked their two sons -- Gerald, then 11, and Christian, 9 -- if they would participate in the Moderna vaccine trial.
"Educating them and getting them on board -- yeah, that took a little bit of convincing," Mugera said, especially given a fear of needles.
Their mother "explained how it works, what it does, how it protects you, and how you get your life back. You can travel. Go back to having birthday parties. Go back to school (in-person)," Mugera said.
"That crystallized in their minds very quickly that this is the path to normalcy."
But because the trial requires blood draws to monitor for antibodies, and Gerald had difficulty getting blood drawn, only Christian was selected for the trial.
The 9-year-old has received both doses of the Moderna vaccine -- the full adult dosage each time.
Christian had a sore arm after his first dose and a fever, muscle aches and lethargy after his second dose. But 24 hours later, he was fine.
Mugera admits the family was on high alert for anything that might resemble an adverse side effect. He got nervous when Christian developed a rash.
"Initially we were like, oh my goodness, is this something from the vaccine?" he said.
But Gerald -- who was not vaccinated -- later broke out with the same rash. It turned out to be contact dermatitis after both boys played outside and climbed a tree.
Gerald recently turned 12 and was able to get the Pfizer vaccine. Now the entire family is looking forward to an overseas vacation.
Though Christian was initially hesitant to get vaccinated, he's now excited to play with friends without masks and go back to his normal childhood without worry, Mugera said.
He's also proud to help other kids by testing the vaccine for them. Christian's dad said his younger son has developed a new mantra:
"We're going to save the world. We're going to change the world."
