Pfizer Inc. and partner BioNTech SE agreed to supply an additional 100 million doses of their COVID-19 vaccine to the U.S.

The agreement brings the total number of doses to be delivered to the U.S. to 200 million, the companies said Wednesday in a statement. The drugmaker expects to deliver all the doses to U.S. vaccine and drug accelerator Operation Warp Speed by July 31.

The pact expands the number of shots that will be available to the government as it ramps up its immunization drive in the coming year. In July, the U.S. had agreed to pay US$1.95 billion for an initial 100 million doses from Pfizer, with an option to buy 500 million more.

The U.S. will also pay US$1.95 billion for the new order, according to the statement.

Pfizer shares gained 0.6 per cent in premarket trading on Wednesday in New York.