WASHINGTON — As nations around the world race to lock up coronavirus vaccines even before they are ready, the Trump administration on Wednesday made one of largest investments yet, announcing a nearly $2 billion contract with Pfizer and a German biotechnology company for 100 million doses by December.

The contract is part of what the White House calls the Warp Speed project, an effort to drastically shorten the time it would take to manufacture and distribute a working vaccine. So far, the United States has put money into more than a half dozen efforts, hoping to build manufacturing ability for an eventual breakthrough.

Europe has a parallel effort underway. Germany recently took a 23% stake in a German firm, CureVac, that President Donald Trump once tried to lure to American shores in hopes that its vaccine, if successful, would be distributed in the United States first. A European-led fundraising effort in May brought $8 billion in pledges from the world’s governments, philanthropists and leaders for coronavirus vaccine research, even with the United States sitting out the conference.

China, meantime, has militarized the effort: Researchers associated with the Academy of Military Medical Sciences have developed one of China’s leading vaccine candidates, and another Chinese firm, Sinopharm Group, announced in June that it was beginning Phase 3 trials in the United Arab Emirates.

The Pfizer contract, an agreement to ensure the pharmaceutical giant has a market for its work, is the biggest splash yet by the Americans. If the vaccine being produced by Pfizer and BioNTech, the German firm, proves to be safe and effective in clinical trials, the companies say they could manufacture those first 100 million doses by the end of the year.

Under the arrangement, the federal government would obtain that first batch for $1.95 billion, or about $20 a dose, with the rights to acquire up to 500 million more, or 600 million total. Americans would receive the vaccine for free. Before it could be distributed, it would need emergency approval by the Food and Drug Administration. But the U.S. government does not pay the nearly $2 billion until the drug is approved and the first 100 million doses are delivered.