WASHINGTON — The United States has given the final go-ahead to the nation’s first COVID-19 vaccine, marking what could be the beginning of the end of an outbreak that has killed nearly 300,000 Americans.

Vaccine distribution for health care workers and nursing home residents are expected to begin in the coming days after the Food and Drug Administration on Friday authorized an emergency rollout of what promises to be a strongly protective vaccine from Pfizer and its German partner BioNTech.

Initial doses are scarce and rationed as the U.S. joins Britain and several other countries in scrambling to vaccinate as many people as possible ahead of winter.

It will take months of work to tamp down the coronavirus that has surged to catastrophic levels in recent weeks and claimed 1.5 million lives globally.