President Biden said the U.S. has struck deals to purchase 200 million more Covid-19 vaccine doses, following a pledge in January to boost the number of shots available for Americans.

Mr. Biden said in a speech at the National Institutes of Health in Bethesda, Md., that the U.S. signed contracts with Pfizer Inc. and Moderna Inc. that require each company to provide an additional 100 million vaccine doses.

“We have to stay vigilant, we have to stay focused and for God’s sake, we have to remember who we are. We are the United States of America. We can do this,” the president said.

The additional vaccines will bring the total number of doses ordered by the U.S. from the two companies to 600 million from 400 million.

The administration said in January that it was working on the purchases, which would provide enough supply to vaccinate 300 million Americans in a two-dose regimen, covering all individuals in the U.S. currently eligible to receive the vaccine.

The vaccine hasn’t been approved for people under 16 years old.