WASHINGTON — The Biden administration is preparing to ship COVID-19 vaccines to the states as quickly as possible, should the Food and Drug Administration approve an emergency use authorization for kids under 5.

White House Coronavirus Response Coordinator Jeffrey Zients said Wednesday that approval of the specially formulated vaccine would make 18 million young children eligible for the first time since the pandemic began two years ago.

“Following FDA authorization, we would immediately begin packing and shipping doses to states and health care providers,” Zients said, noting the federal government has already “secured ample doses and the necessary needles and supplies” designed for this age group.

If the FDA and the Centers for Disease Control and Prevention give the vaccine the green light, Zients said he expects it would take several days or a week before the first shots could begin. That timetable, he said, is similar to what the White House experienced when authorizers approved vaccines for children between the ages of 5 and 11 in October.

Since then, just over 8 million of the 28 million children in that age group have received at least one dose of the vaccine, according to the Kaiser Family Foundation.

Zients seemed to acknowledge there may be parents somewhat hesitant to get their young children vaccinated and said the White House is preparing to address concerns.

“While we know many parents are eager to get their kids the protection of the vaccine, we know others have questions,” Zients said. “So we’re working with our partners to make sure parents have access to the facts.”

Surgeon General Vivek H. Murthy sought to address why it is that Pfizer and BioNTech began the process for an emergency use authorization on Tuesday, despite saying in mid-December its two-dose regimen for children between 2 and 4 didn’t produce the type of immune response its researchers wanted.

“There’s a big change that’s happened and that’s that we experienced the omicron surge,” Murthy said. “It turns out that has actually facilitated the collection of important clinical data, additional clinical data that we did not have in December.”

“Whether that changes the risk-benefit profile is what the FDA will be assessing, but there has been developments since December,” Murthy continued.

Anthony Fauci, director of the National Institute for Allergy and Infectious Disease, said he didn’t want to get ahead of the FDA but said he expected “a vaccine efficacy signal that would allow for the use of this vaccine in children.”

The two companies announced Tuesday that while they are seeking emergency authorization for two shots, researchers plan to continue gathering data on a third dose that would likely be administered at least eight weeks after a child receives the second dose.

Pfizer Chairman and Chief Executive Officer Albert Bourla said in the statement that the company believes ultimately “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.”