Vaccine doses for children under 5 years old are likely to receive a green light within the next week, but the Philadelphia Department of Public Health is warning there may be a lag before the shots are available locally.

Many doctors’ offices are waiting for an advisory panel at the Food and Drug Administration to give their approval to the vaccines developed by Moderna and Pfizer before placing orders for the doses, the health department said Monday in a news release.

The federal panel is holding hearings Tuesday and Wednesday on the safety and efficacy of various pediatric vaccines. If the FDA, along with the Centers for Disease Control and Prevention, authorize the rollout of vaccines for young children, federal health officials have said the first 10 million doses could be available as soon as June 21.

Some physician’s offices, though, may not receive doses that soon if they’re waiting to hear the results of this week’s hearings, the city health department advised.

“Being aware that the efficacy data won’t come out until tomorrow, we made the educated guess that many vaccine providers might prefer to wait before ordering,” said James Kyle, a spokesperson for the health department. “We intend to put out more information tomorrow after the data comes.”

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Doctors’ offices have been vital throughout the vaccination process, but will be particularly important participants in the effort to inoculate the last large group of Americans to be eligible for the shots. Children younger than 2 years old can’t receive doses from pharmacists, meaning pediatricians will be relied on heavily to give shots to that age group.

Doctors and public health experts are anticipating an early surge of parents eager to get their youngest children vaccinated, followed by some of the same hesitancy that has accompanied the vaccination effort for older children. Just one in five parents was planning to immediately get their young children vaccinated, according to a national survey released last month by the Kaiser Family Foundation, a nonprofit health organization. More than a third wanted to wait and see how other children responded before getting doses for their own.

The FDA has already said Pfizer and Moderna’s doses for children are safe and effective. The first two Pfizer doses — each a tenth of the dose adults receive — are to be delivered within three weeks of each other, with the third coming two months later. Its studies show the series is about 80% effective at preventing illness. The Moderna vaccine comes in two doses given four weeks apart. Trials have shown it to be 51% effective at preventing mild illness for children 2 and younger, and 37% effective for children between ages 3 and 5.