Dr. Rochelle Walensky, the U.S. Centers for Disease Control and Prevention (CDC) director, said Tuesday that nearly 600,000 children between the ages 12 and 15 have received their first dose of the Pfizer-BioNTech COVID-19 vaccine.

This figure has come just over a week after the U.S. Food and Drug Administration (FDA) granted Emergency Use Authorization (EUA) of the vaccine in this age group, which accounts for a total of 17 million in the U.S.

Major pharmacies and hospitals did not start administering the shots until last Thursday after the CDC also recommended the use of the vaccine in this age group.

Only Pfizer-BioNTech’s COVID-19 vaccine has been approved for use in children under 18.

The CDC said that about 3.5 million people younger than 18 have been vaccinated as of Tuesday.

The American Academy of Pediatrics (AAP) said nearly 4 million cases of the COVID-19 had been reported among children as of May 13, representing about 14% of all COVID-19 cases in the U.S.

Younger people have a relatively lower risk of developing severe COVID-19 illness than older adults, but in some cases, they have become very ill, with officials reporting 308 deaths in children.

It has also been found that nearly 3,700 children with the COVID-19 infection went on to develop multisystem inflammatory syndrome (MIS).

In children, MIS generally develops several weeks after a minor case of the illness and results in inflammation of various organs, including the heart, lungs, kidneys, the brain, and the gastrointestinal system, according to TODAY.

Some members of the Biden administration have strongly encouraged vaccinations in young people.

Andy Slavitt, White House COVID-19 adviser said Tuesday, “The pandemic disrupted your schooling, your job search, your income, your social lives. You’ve seen and experienced stress in a way you probably haven’t before.”

“Your generation has shown us how you make the world a better place,” he added. “Getting vaccinated is part of carrying the mantle of becoming the generation that changes things for the better.” This story appeared on NBC News and TODAY.