$MRNA The U.S. government has exercised an option to buy an additional 100 million doses of Moderna's Covid-19 vaccine, doubling the contracted supply to 200 million doses by the end of June 2021 if the shot is authorized, the government and the company said Friday. Moderna said the government is paying $1.65 billion for the new doses. The added supply will bolster the vaccination campaign that is about to get under way in the U.S. The Food and Drug Administration is expected imminently to authorize the first Covid-19 vaccine from Pfizer and BioNTech, which are planning to provide 100 million doses for use in the U.S.