The United States on Wednesday announced an agreement with Pfizer and BioNTech for 105 million doses of Covid vaccine for Americans this fall.

The $3.2 billion contract, signed between the companies and the US health and defense departments, includes vaccines for babies, young children, teens and adults, and may include Omicron-specific vaccines, which a panel of government experts recommended on Tuesday.

Delivery will begin in late summer and continue into the fourth quarter, the companies said. The contract gives the US the option to procure up to 300 million doses.

"The Biden-Harris Administration is committed to doing everything we can to continue to make vaccines free and widely available to Americans - and this is an important first step to preparing us for the fall," Health and Human Services Secretary Xavier Becerra said in a statement.

President Joe Biden's administration has asked Congress for $23.5 billion in additional Covid funding, but a bill has not yet been passed.

As a result, the federal government "was forced to reallocate $10 billion in existing funding, pulling billions of dollars from Covid-19 response efforts" the statement said, with the new vaccines procured through this reallocation.

White House officials have previously said that without new funding, future vaccines might only be given for free to those at highest risk.