As the COVID-19 vaccine rollout steadily steams ahead, one population is still left without one: children and adolescents.

Now, with months of vaccine clinical trial data under their belts, pharmaceutical companies are getting closer to offering the same protection for kids.

The U.S. Food and Drug Administration is expected to authorize Pfizer-BioNTech's coronavirus vaccine for ages 12-15 soon, with some reports indicating the approval could come in early May.

"With any medication trial, kids are seen as a vulnerable population because their immune systems are more naïve and extra safety measures are always taken," says Terri Stillwell, M.D., M.P.H., pediatric infectious disease expert and associate hospital epidemiologist at Michigan Medicine C.S. Mott Children's Hospital.

"We've now administered millions of doses of vaccines, which clearly gives us a good baseline of overall safety data. As vaccine safety and efficacy becomes well established in adults, the same vaccines can safely be tested in younger children."

Vaccine side effects are usually comparable between adults and kids, but researchers must test the new vaccine in children to know for sure whether it will generate the same immune response, Stillwell says.

Although severe COVID disease is still rare among pediatric populations, some children do develop more serious and life-threatening complications, including multi-system inflammatory syndrome, or MIS-C. A growing number of states have reported MIS-C cases among kids, which causes severe inflammation in vital organs and tissues.

Children with underlying conditions are also at higher risk of severe disease and hospitalization.

"While rare, children across the country have gotten very sick or died from COVID complications," Stillwell says. "Even one child is too many."

Kids also make up nearly a fifth of the population, which means vaccinating them will be essential to obtaining herd immunity.  

SEE ALSO: COVID Upticks Among Kids and Teens: What Parents Should Know

"Even if they have mild COVID symptoms, children and teenagers can spread the coronavirus to more vulnerable groups," Stillwell says.

"We will need vaccination among all age groups in order to truly control the pandemic. Without a pediatric vaccine, the virus will continue to circulate through communities."

Pediatric vaccines will mean a quicker path to normal kid life as well. COVID exposures have disrupted in-person school where quarantines mean masses of students missing classes. Virus risks also interrupt activities like sports and extracurricular programs and milestones like prom and graduation.

Stillwell discusses what parents and families can expect to see for vaccines in younger groups over coming months.

COVID vaccines for teens 16 and over

In April, the Centers for Disease Control expanded COVID-19 vaccine eligibility from 18 and over to include ages 16 and 17.  

Of the three vaccines authorized in the U.S., the Pfizer-BioNTech shot is currently the only one available for this population. Other drug companies will likely follow suit as they enter phase three of testing in clinical trials.

There aren't too many differences to consider between a 16 and 18-year-old, and it would be expected that the vaccine would work the same for both. But because younger teens are minors, they still need guardian consents.

Teens and young people appear to have played a bigger role in the spring surge, with some COVID clusters in parts of the U.S. being traced back to extracurricular activities, youth sports and socialization.

"We've seen youth cases drive some of the recent outbreaks around the country, so this is an important age group to include in public health efforts to contain spread," Stillwell says.

Adolescents and teens ages 12-15

Pfizer-BioNTech recently sought federal approval to vaccinate younger age children after a trial showed the vaccine currently used in adults was also effective in 12-15 year olds. The FDA will reportedly authorize the vaccine for that age group in coming weeks.

The pharmaceutical company reports the vaccine has showed 100% efficacy and robust antibody responses for this pediatric population. The more than 2,200 trial participants will continue to be followed for two years after their second dose to ensure safety and vaccine durability.

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Moderna has also completed enrollment of 3,000 participants in its study of the COVID-19 vaccine for youth aged 12 to 17.

"Adolescents and younger teens are next in line," Stillwell says. "We expect the vaccine to be available to them before the start of the next school year."

COVID vaccines for younger children  

Both Pfizer and Moderna are enrolling children younger than 12 for early phase trials to determine safety in dosing and immune responses.

These trials will likely mimic early trials in adults, Stillwell says, beginning with recipients on the older side of the spectrum and eventually including children as young as six months old.

SEE ALSO: MIS-C: The COVID-Related Condition Parents Need to Know About

At this phase, because evidence now supports the vaccine's overall safety, trials will focus on determining appropriate dosing.

It's a little bit of the Goldilocks strategy, testing a range of doses to find one that is effective and triggers a strong immune response without too many side effects.

"The goal is to find that sweet spot that's just right for children," Stillwell says.

It will take longer to test dose adjustments to see whether lower doses will invoke equal responses, she says. Experts have predicted that vaccines for younger children ages 5-12 could be ready anywhere between late 2021 and early 2022, followed by vaccines that may be used in toddlers and babies.

"Great vigilance goes into developing drugs and vaccines for pediatric populations," Stillwell says. "Children in these trials will be followed for months or even years to study safety and effectiveness."

She notes that timing of these vaccine rollouts will also depend on pandemic activity. Researchers will need to be able to observe immune responses when the virus is still circulating in order to obtain necessary data for federal approvals.  

But developing effective vaccines for all age groups will be a critical piece of the pandemic puzzle when it comes to combating COVID long term.

"It's important not to leave any population vulnerable to this virus," Stillwell says.

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