By Carl O’Donnell

(Reuters) -The United States administered COVID-19 vaccinations to around 600,000 children ages 12 to 15 last week after regulators cleared Pfizer Inc’s and BioNTech’s shots for use in that age group, U.S. Centers for Disease Control and Prevention Director Rochelle Walensky said in a media call on Tuesday.

In total, more than 4 million people under 17 have been vaccinated in the United States so far, she added. Top U.S. infectious disease specialist Anthony Fauci said he expects that by the end of 2021 the United States will have enough safety data to vaccinate children of any age.

U.S. regulators last week authorized Pfizer’s COVID-19 vaccine for use in children as young as 12. Most states began issuing shots to children last Thursday but some, including Georgia, started sooner.

Pfizer’s shot is the first to be cleared in the United States for children 12 to 15. Vaccinating younger ages is considered important for getting children back into schools safely. U.S. President Joe Biden has asked states to make the vaccine available to younger adolescents immediately.

The vaccine has been available under an emergency use authorization to people as young as 16 in the United States since December.

Most children with COVID-19 develop only mild symptoms or no symptoms. Yet children remain at risk of becoming seriously ill, and they can spread the virus.

Widely vaccinating 12- to 18-year old’s could allow U.S. schools and summer camps to relax masking and social distancing measures suggested by the CDC.

Fauci also said on Tuesday that existing COVID-19 shots probably also protect against the new variant of the coronavirus first found in India, which has been battling the world’s biggest jump in COVID-19 infections.

(Reporting by Carl O’Donnell, additional reporting by Jeff Mason; Editing by Chizu Nomiyama and David Gregorio)