(NEXSTAR) – Dr. Anthony Fauci said Tuesday that children will likely begin receiving COVID-19 vaccines in the fall.

Speaking to the Wall Street Journal, the nation’s top infectious disease expert said, “We will get children of high school age — 12 to 17 — to get vaccinated by the fall.”

Younger children will likely have to wait longer. Fauci predicted that those under the age of 12 may start receiving the COVID-19 vaccine “in the first part of the first quarter of 2022.”

About 22 percent of American adults have received at least the first dose of the vaccine, as of Tuesday, the Centers for Disease Control and Prevention said.

Moderna announced Tuesday that it had begun testing a COVID-19 vaccine on children.

“We are pleased to begin this Phase 2/3 study of mRNA-1273 in healthy children in the U.S. and Canada and we thank NIAID and BARDA for their collaboration,” said Stéphane Bancel, chief executive officer of Moderna.

“It is humbling to know that 17.8 million adults in the U.S. have received the Moderna COVID-19 Vaccine to date. We are encouraged by the primary analysis of the Phase 3 COVE study of mRNA-1273 in adults ages 18 and above and this pediatric study will help us assess the potential safety and immunogenicity of our COVID-19 vaccine candidate in this important younger age population.”

The first participants are at least 6 months old and younger than 12 years old. In the study, the children are given two doses, 28 days apart.

More than 6,000 healthy children in the U.S. and Canada will be enrolled in the study, which will “evaluate the safety, tolerability, reactogenicity and effectiveness” of the vaccine in children. Reactogenicity refers to what the possible “expected” symptoms might be, such as a sore arm, tiredness or a fever.