(The Center Square) – Distribution of a new COVID-19 vaccine is now underway after the U.S. Food and Drug Administration late Friday granted emergency use authorization for the serum.

Pfizer's and BioNTech’s coronavirus vaccine is the first to receive the authorization and vaccinations are expected to begin as soon as this weekend.

"With this authorization, we know that our federal partners are already moving to distribute the first doses of the vaccine throughout the country," FDA Commissioner Dr. Stephen Hahn said at a Saturday morning news conference.

Calling the development of the vaccine in less than a year an "unparalleled scientific achievement," Hahn said collaboration between the private sector, the scientific and academic community and the federal government allowed the process to move efficiently but safely.

"Efficiency does not mean cutting of corners," Hahn said, noting that studies and testing are ongoing.

"What's different during COVID-19 is that developers, researchers and regulators have found new and hopefully lasting ways to be dynamic and efficient," he said.

FDA officials said millions of doses would ship within the first 24 hours after approval. The doses would be prorated by population, with health care workers and residents and staff of congregate care settings such as nursing homes among the first to receive the shots.

Pfizer has said that its vaccine, which is to be administered in two doses about three weeks apart, is more than 95 percent effective.

Moderna is expected to receive approval for its vaccine when the FDA reviews its emergency authorization Dec. 17. AstraZenica and Johnson & Johnson also have vaccines in the accelerated approval pipeline.