And then there were three: A single-shot vaccine is the latest weapon to join the battle against COVID-19 in the United States.

On February 27, the U.S. Food and Drug Administration gave emergency use authorization for Johnson & Johnson’s vaccine against SARS-CoV-2, the coronavirus that causes COVID-19. South Africa is the only other country to OK Johnson & Johnson’s vaccine so far, though other countries are poised to follow suit.

The FDA determined that Johnson & Johnson’s vaccine meets the criteria for safety and effectiveness and that there is clear evidence that it may prevent COVID-19, the agency said in a statement.

“With today’s authorization, we are adding another vaccine in our medical toolbox to fight this virus,” said Peter Marks,  director of the FDA’s Center for Biologics Evaluation and Research.

Its authorization for emergency use in the United States – for people age 18 and older – follows similar authorizations in December for vaccines made by Moderna and by Pfizer and its German partner BioNTech.

Shortages of vaccines make the addition of a third safe and effective vaccine welcome. “We’re still in the midst of this deadly pandemic,” says Archana Chatterjee, Dean of the Chicago Medical School at Rosalind Franklin University of Medicine and Science.

“Authorization of this vaccine will help meet the needs at the moment,” she said February 26 after an FDA vaccine advisory committee unanimously voted to recommend Johnson & Johnson’s vaccine for emergency use.

But even as the pharmaceutical company readies to ship out 4 million doses, questions remain about how well the public will embrace the new shot.

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