BREAKING: Biden announces purchase of 100 million Johnson & Johnson COVID-19 vaccine doses

President Joe R. Biden announced that his administration had ordered an additional 100 million doses of the single-dose Johnson & Johnson COVID-19 vaccine.

Biden announced the purchase during an event with the CEOs of Johnson & Johnson and Merck in which he echoed a claim he made earlier that the nation is on course to having enough vaccine doses for all Americans by the end of May.

"I'm doing this because this wartime effort needs maximum flexibility," Biden said. "There's always a chance we will encounter unexpected challenges or there'll be a new need for a vaccination effort. A lot could happen, a lot could change, and we need to be prepared."

The additional doses will be a welcome addition to the vaccination effort which has ramped up in recent weeks. Previously, Biden announced his administration had negotiated a deal in which Merck would manufacture doses of the Johnson & Johnson vaccine, after the drug making rival failed to develop its own.

The Food and Drug Administration granted the Johnson & Johnson vaccine emergency use authorization in late-February, making it the third authorized vaccine for COVID-19.

The FDA released documents ahead of a Feb. 26 meeting of the Vaccines and Related Biological Products Advisory Committee detailing the vaccine’s effectiveness against the disease. They said that it was shown to be 66.9 percent effective against moderate to severe or critical COVID-19 and is 76.7 percent effective in preventing severe or critical instances of the disease.

The documents note that the vaccine has been highly effective in the prevention of severe or critical COVID-19 caused by emerging strains of the disease with 73.1 percent efficacy in South Africa. This is a 7 percent increase in efficacy against the South African strain of the disease from what the company believed in January.