When can children younger than 5 get vaccinated against Covid-19?

Children younger than 5 in the United States could begin receiving Covid-19 vaccinations this month or next if the US Food and Drug Administration moves quickly to authorize the shot for this age group.On Tuesday, vaccine makers Pfizer and BioNTech initiated a request for the FDA to authorize their child-sized coronavirus vaccine for emergency use in the United States among children age 6 months to up to 5 years.

The Pfizer/BioNTech vaccine is already authorized for use in people as young as 5, and if authorized, this shot will be the first coronavirus vaccine available for the youngest children.

The companies asked the FDA to grant emergency use authorization for a two-dose regimen of the vaccine. Meanwhile, the vaccine makers plan to continue testing a three-dose regimen in this younger age group.

"As hospitalizations of children under 5 due to COVID-19 have soared, our mutual goal with the FDA is to prepare for future variant surges and provide parents with an option to help protect their children from this virus," Pfizer Chairman and CEO Albert Bourla said. "Ultimately, 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."

What happens next could determine how soon parents can get their toddlers vaccinated.

What needs to happen before shots can roll out? Before the Pfizer/BioNTech coronavirus vaccine can be administered to children under 5, the FDA needs to authorize it for emergency use among that age group.

Once the FDA authorizes the vaccine for young children, vaccine advisers to the US Centers for Disease Control and Prevention -- the Advisory Committee on Immunization Practices -- would meet to discuss the EUA, review data on the vaccine and vote on advising the CDC to recommend using the vaccine.

"The FDA uses data submitted by the manufacturer. ACIP can use all kinds of other data to consider in their deliberations," Dr. Sean O'Leary, vice-chair of the American Academy of Pediatrics Committee on Infectious Diseases, told CNN on Tuesday.

Next, CDC Director Dr. Rochelle Walensky reviews ACIP's vote and could recommend the vaccine for children under 5, giving the green light for vaccines to be administered to that age group.

"At that point, then, it just depends on getting the vaccine shipped into places that they're going to be delivering the vaccine," said O'Leary, who is also a professor of pediatric infectious disease at the University of Colorado School of Medicine and works with Children's Hospital Colorado.

Federal regulators encouraged Pfizer to seek authorization for a two-dose vaccine regimen, which would allow an EUA to possibly be granted by late February, according to a person familiar with the plan. Waiting on data for three doses could extend the wait until March.

This means young children age 6 months to up to 5 years could get vaccinated as early as sometime in late February or early March.

In December, Pfizer announced that it decided to add a third dose to the primary vaccine regimen for babies and children ages 6 months to up to 5 years. That decision came after initial trials in children ages 2 to 5 showed that the original two-dose regimen of the child-sized vaccine did not provide the expected immunity in the 2- to 5-year-olds, although it did so for the babies up to age 2.