The U.S. purchased an additional 200 million doses of Pfizer's COVID-19 vaccine, the drugmaker said July 23.
Pfizer expects to deliver 110 million doses by Dec. 31, with the remaining 90 million doses expected to be delivered by April 30.
The U.S. also has the option to obtain an updated version of the vaccine designed to target coronavirus variants, should one be authorized.
The deal brings the total number of Pfizer doses purchased by the U.S. government to 500 million.