A nurse prepares the Pfizer-BioNTech Covid-19 vaccine for children for...

A nurse prepares the Pfizer-BioNTech Covid-19 vaccine for children for distribution in Montreal, Quebec, this past November. Credit: AFP via Getty Images / Andrej Ivanov

Children as young as 6 months could soon be eligible for the COVID-19 vaccine if federal regulators agree the shots are safe and effective.

Pfizer-BioNTech this week asked the U.S. Food and Drug Administration to approve two doses for children ages 6 months to 4 years old, with the expectation that a third dose would be needed shortly thereafter. The vaccine is already available for children 5 and up.

Here's everything you need to know about the process:

How soon could the vaccine be available to children under age 5?

Approval could come as soon as this month. An FDA advisory panel is set to meet Feb. 15 to consider Pfizer's safety and efficacy data. The FDA would vote for approval next, followed by a Centers for Disease Control and Prevention advisory group and final approval from CDC Director Rochelle Walensky.

The initial approval would be for two doses while Pfizer conducts clinical trials on the efficacy of a third shot.

Moderna is also testing its vaccine with this age group and plans to submit data to the FDA in March. Johnson & Johnson is also expected to conduct vaccine trials for younger kids.

What have Pfizer's pediatric clinical trials shown?

The trials of approximately 8,300 children from 6 months to 12 years old showed varying immune responses for kids of different ages.

Children ages 6 months to 2 years showed better protection, Pfizer found, but the two-dose regimen failed to provide robust immunity to kids ages 2 to 4.

"The dose we were giving to these younger kids was safe, but not necessarily enough to provide sufficient protection against COVID," said Dr. Andrew Handel, assistant professor of pediatric infectious diseases at Stony Brook Children’s Hospital, which is conducting trials on a three-dose regimen for young children.

Pfizer is investigating providing younger children a series of three shots, with the second coming 21 days after the first, and the third eight weeks later.

"We believe that three doses of the vaccine will be needed for children 6 months through 4 years of age to achieve high levels of protection against current and potential future variants," Albert Bourla, chairman and chief executive of Pfizer, said this week. "If two doses are authorized, parents will have the opportunity to begin a COVID-19 vaccination series for their children while awaiting potential authorization of a third dose."

Why is a vaccine for children this young necessary?

Since the start of the pandemic, 10.6 million children have tested positive for COVID, including about 1.6 million under the age of 4, leading to 287 deaths in that age group, according to CDC data. The American Academy of Pediatrics said children account for almost one-quarter of new COVID infections.

And while younger children typically have milder infections, experts suggest vaccinating younger children can help control the spread of the virus to older and more vulnerable Americans, allow schools to remain open and reduce the stress on health care facilities.

Will young children be given the same amount of vaccine as older children or adults?

No. The dose for children 6 months to age 4 years would be 3 micrograms. Comparatively, children ages 5-11 receive a 10-microgram dose and those 12 and older receive 30 micrograms.

Will parents ultimately get their youngest children vaccinated?

That remains unclear. A poll published this week by the Kaiser Family Foundation found that 31% of parents of children under 5 would immediately vaccinate their kids. Nearly a third said they would take a wait-and-see approach while 38% said they would not vaccinate their children or only do so if required.