Parents may be able to vaccinate their youngest kids as early as June 21, officials say. Here's what to know.

Parents eager to vaccinate their youngest children may be able to do so as early as June 21, a top White House pandemic advisor said during a briefing Thursday.

Dr. Ashish Jha, coordinator of the federal COVID-19 response, told reporters the Biden administration is working closely with states, pharmacies and other health care providers to prepare for authorization from key regulatory agencies.

"We know that many many parents are eager to vaccinate their youngest kids and it's important to do this right," Jha said.

The news comes a week after Pfizer and German partner BioNTech announced their vaccine for kids under 5 appeared to be safe and effective.

The companies have been testing their COVID-19 vaccine in this age group since last year. Their research suggested two shots would not be enough to prevent illness during the omicron outbreak, so the companies added a third shot to the regimen.

Fellow vaccine developer Moderna also released trial data in March showing their low-dose two-shot vaccine was also safe in children 6 months up to 6 years. In late April, the company submitted a request to the Food and Drug Administration for emergency use authorization in that age group.

As the pharmaceutical companies await FDA review in the coming weeks, here’s what you need to know about their vaccines and when they could be available.

When will a COVID vaccine be available for kids under 5?

An FDA advisory committee plans to meet June 15 to discuss both vaccines for kids as young as 6 months.

Pfizer and BioNTech have not yet provided their complete data to the FDA but expect to within about a week, according to the companies. Moderna said it completed its application for the youngest children last month.

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Assuming the committee recommends one or both vaccines and the FDA authorizes them, an advisory committee with the Centers for Disease Control and Prevention will evaluate the data before it would need to be signed off by the agency's director, Dr. Rochelle Walensky.

Pfizer COVID vaccine in kids: What does the data say?

Pfizer-BioNTech's COVID-19 vaccine is authorized in the U.S. for everyone ages 5 and over.

The companies released a study Monday of nearly 1,700 children under 5 showing their low-dose vaccine was as safe as a placebo and more than 80% protective during the omicron outbreak.

Effectiveness is still unconfirmed in this age group, awaiting more infections, but only 10 children in the trial developed symptomatic cases as of April 29, the companies said. The trial protocol specified that a formal effectiveness analysis would be done once at least 21 children developed symptomatic cases.

The Pfizer-BioNTech vaccine for children under 5 is identical to but one-tenth the dose of vaccines for adults and teens.

How effective is the Moderna COVID vaccine?

Moderna submitted a request for emergency use authorization for its two-dose COVID-19 vaccine for children 6 months through 5 years old in late April.

In the company’s study of 6,700 kids, researchers found after receiving two low doses of the vaccine they developed levels of virus-fighting antibodies comparable to young adults who received two doses of the full-strength shot.

In the Phase 3 study, which took place during the omicron wave, researchers found the vaccine was 51% effective among children 6 months to under 2, and 37% effective among children 2 to under 6.

The company’s chief medical officer Dr. Paul Burton told USA TODAY effectiveness may be less in the older group because of their changing immune systems.

Is the COVID vaccine safe for kids under 5?

Pfizer and BioNTech said their trial in small children identified no new safety concerns and the majority of reported adverse events were mild or moderate.

Federal officials were initially concerned that the Moderna vaccine was associated with an increased risk of a heart condition, called myocarditis, and haven't authorized the the company's vaccine for anyone under 18.

After nearly a year's worth of data and review, the FDA's advisory committee will meet to discuss the company's vaccine for children ages 6 to 18 on June 14, a day before discussing the vaccine for children under 6.

Is the children’s Pfizer COVID-19 vaccine different than the adult one?

The Pfizer-BioNTech vaccine is the only COVID-19 vaccine currently authorized for children. Kids ages 5 through 11 receive one-third the adult dose. They have been authorized for a two-dose regimen as well as a booster shot.

The dose for children under 5 is 3 micrograms, one-tenth the size of the adult dose. It would be given as a three-dose regimen.

What are the common side effects of the vaccine in young children?

The most common side effects after a Pfizer shot are pain, redness or swelling where the shot was given; tiredness; fever; or a headache – all of which typically resolve within a few days. Moderna reported similar side effects.

Can kids get the second vaccine if they had COVID-19 in between?

Children who are experiencing symptoms or test positive for COVID-19 should wait until after they recover to receive their second shot, the CDC says.

Many act like the pandemic has ended: That's not an option for the immunocompromised.

Health experts say it's important for children to get vaccinated after they've recovered from COVID-19 as added protection against the virus.

A study published in an April Morbidity and Mortality Weekly Report found adults who had COVID-19 before were up to 68% protected against reinfection during the omicron wave if they were vaccinated and boosted compared to those who were not vaccinated.

Where can I get the COVID-19 vaccine for my child?

Major pharmacies in the country currently carry Pfizer's vaccine for children 5 and older, and Moderna's vaccine for adults.

Walgreens and CVS, the biggest pharmacies in the U.S., say they're preparing to carry COVID-19 vaccines for children under 5. After previous federal sign-offs, vaccine doses were available at local pharmacies and doctors' offices as soon as a few days after authorization.

Parents can also get their children vaccinated at their pediatrician's office, health experts say. Younger children in particular may be more comfortable receiving a shot in a familiar place from someone they recognize.

Contributing: Karen Weintraub and Elizabeth Weise, USA TODAY. Follow Adrianna Rodriguez on Twitter: @AdriannaUSAT.

Health and patient safety coverage at USA TODAY is made possible in part by a grant from the Masimo Foundation for Ethics, Innovation and Competition in Healthcare. The Masimo Foundation does not provide editorial input.

This article originally appeared on USA TODAY: COVID vaccine kids under 5: What to know about Pfizer, Moderna doses