WASHINGTON (NewsNation Now) — The U.S. Food and Drug Administration authorized Johnson and Johnson’s single-dose COVID-19 vaccine for emergency use Saturday, making it the third vaccine available in the United States and the first that only takes one dose to protect against the coronavirus.

An FDA panel of U.S. health advisers unanimously endorsed the one-dose vaccine on Friday. A few million doses of the new vaccine could begin shipping as early as Monday.

The company has said it can deliver 20 million doses by the end of March and a total of 100 million by the end of June, keeping President Joe Biden on track for his vaccination goal.

On Sunday, a U.S. advisory committee will meet to recommend how to prioritize use of the single-dose vaccine.

More than 66 million COVID-19 vaccine shots have been administered in the U.S. to date, according to the CDC, including 50 million since Biden and Harris entered the White House.

J&J’s vaccine protects against the worst effects of COVID-19 after one shot, and it can be stored up to three months at refrigerator temperatures, making it easier to handle than the Pfizer and Moderna vaccines, which must be frozen.

The two-dose Pfizer and Moderna shots were found to be about 95% effective against symptomatic COVID-19 while the J&J vaccine was 85% protective against the most severe COVID-19 and 66% effective in moderate cases.

While the FDA found J&J’s vaccine safe and effective, some experts fear that lower effectiveness could feed public perceptions that J&J’s shot is a “second-tier vaccine.”

J&J’s vaccine was tested in the U.S., Latin America and South Africa at a time when more contagious mutated versions of the virus were spreading. That wasn’t the case last fall when Pfizer and Moderna were wrapping up testing, and it is still not clear if their numbers would hold against the most worrisome of those variants.

FDA finds Johnson & Johnson’s one-shot COVID-19 vaccine effective and safe 

The United States has an agreement to buy 100 million doses of J&J’s vaccine for $1 billion, and the option of purchasing an additional 200 million doses. J&J said it aims to deliver 1 billion doses in 2021 with production in the United States, Europe, South Africa and India.

President Biden applauded the news in a statement Saturday but urged Americans not to let their guards down in preventing the spread of the virus.

“Today, after a rigorous, open, and objective scientific review process, the Food and Drug Administration issued an emergency use authorization for a third safe and effective vaccine to help us defeat the COVID-19 pandemic — the Janssen COVID-19 (Johnson & Johnson) vaccine,” Biden said. “This is exciting news for all Americans, and an encouraging development in our efforts to bring an end to the crisis.”

The third vaccine is expected to speed up vaccination efforts amid setbacks caused by winter storms across the country.

So far, the virus has killed more than 500,000 Americans.