CNN  — 

Approximately 900,000 children ages 5 through 11 are expected to have received a first dose of the Pfizer Covid-19 vaccine by the end of Wednesday, a White House official said. An announcement is expected to come later today.

About 700,000 appointments have been made at pharmacies for upcoming days, the official added.

The new figures come just one week after the Covid-19 vaccine became available for this age group. The White House has worked with pediatricians, pharmacies, children’s hospitals, community health centers, schools and other organizations to launch the vaccination program for kids ages 5 to 11.

“Parents and families across the country are breathing giant sighs of relief. And we are just getting started,” the official said.

Health officials are expected to tout efforts like those in Minnesota, which opened more than 1,100 locations for kids vaccine, including a state-run site at the Mall of America, where more than 1,500 kids can be vaccinated a day; at 114 children’s hospitals that are now offering vaccinations; at mobile clinics in several states; and in New York City, which has more than 1,000 clinics planned at schools in every borough.

About 20,000 vaccination sites are already operational for children 5 to 11 years old.

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First lady Jill Biden and US Surgeon General Dr. Vivek Murthy this week kicked off a nationwide effort to encourage vaccines for the youngest groups eligible, including a push for more vaccination sites. Biden will be visiting sites at schools, children’s hospitals and other sites.

US Health and Human Services Secretary Xavier Becerra and Education Secretary Miguel Cardona also sent a letter on Monday to school superintendents and elementary school principals.

“We urge you to do all you can to help parents and families learn about the vaccine and get access to it,” the secretaries wrote in the letter, encouraging the school leaders to host a Covid-19 clinic at their schools, distribute information to families with children 5 to 11 years old and host conversations with school communities in partnership with medical professionals.