• The FDA has approved J&J's Covid-19 vaccine for emergency use, giving the U.S. a third tool to fight the pandemic.
• Unlike Pfizer's and Moderna's vaccines, J&J's one-dose regimen eliminates the need for patients to return for a second dose and it can be stored at refrigerator temperatures for months.
• The federal government plans to distribute nearly 4 million doses of J&J's vaccine to states, pharmacies and community health centers across the nation next week.

The Food and Drug Administration has approved Johnson & Johnson's Covid-19 vaccine for emergency use, giving the United States a third tool to fight the pandemic as highly contagious variants start to take root across the country.

The FDA's emergency use authorization Saturday kickstarts the federal government's plan to distribute nearly 4 million doses of J&J's vaccine to states, pharmacies and community health centers across the nation next week. Unlike Pfizer's and Moderna's vaccines, J&J's one-dose regimen eliminates the need for patients to return for a second dose and it can be stored at refrigerator temperatures for months.

J&J's vaccine "makes it operationally easier in lots of contexts," Dr. Nancy Messonnier, director of the CDC's National Center for Immunization and Respiratory Diseases, told the Journal of the American Medical Association during a Q&A event on Friday. "I expect lots of considerations state health departments are having around these vaccines is more about the ease of use of the J&J vaccine and how it might be better suited for some populations."

Initially, doses would be limited, J&J has said. The company expects to deliver 20 million doses by the end of March, J&J's vice president of U.S. medical affairs, Dr. Richard Nettles, told House lawmakers on Tuesday. J&J has a deal with the U.S. government to supply 100 million doses of its vaccine by the end of June, and U.S. officials say they are working with the company to ramp up supply as quickly as possible.

In recent weeks, U.S. health officials have pushed Americans to get vaccinated as quickly as possible. Officials are growing concerned about new, emerging variants of the virus, particularly the B.1.351 strain, which has been shown to reduce the effectiveness of vaccines both on the market and under development. On Friday, the head of the Centers for Disease Control and Prevention, Dr. Rochelle Walensky, warned the declines in Covid-19 cases reported in the U.S. since early January may be flattening as variants spread.

J&J submitted its Covid vaccine data to the FDA on Feb. 4. The vaccine's level of protection varied by region, J&J said, with the shot demonstrating 66% effectiveness overall, 72% in the United States, 66% in Latin America and 57% in South Africa, where the B.1.351 variant is rapidly spreading. However, FDA documents show the vaccine was 64% effective in South Africa after about a month. The company said the vaccine prevented 100% of hospitalizations and deaths.

Pfizer's vaccine was found to be 95% effective against preventing Covid-19, while Moderna's was found to be about 94% effective. Infectious disease experts pointed out that J&J's numbers can't be used as a direct comparison to the other two vaccines because it's a single dose and the company's trial was conducted when there were more infections as well as new, more contagious variants.

The FDA has indicated it would authorize a Covid-19 vaccine that's safe and at least 50% effective. The flu vaccine, by comparison, generally reduces people's risk of getting influenza by 40% to 60% compared with people who aren't inoculated, according to the CDC.

The FDA authorized J&J's vaccine for people who are 18 years old and older. It isn't the same as full approval, which requires more data and can typically take several months longer. J&J, like Pfizer and Moderna, has submitted only two months of safety data, but the agency usually requires six months for full approval. The FDA approved the emergency use of hydroxychloroquine to treat Covid-19 in March, only to revoke it in June after additional data showed it provided "no evidence of benefit" in coronavirus patients.

The FDA was expected to approve J&J's vaccine for emergency use.

The agency's announcement comes after a key panel on Friday unanimously backed the vaccine for emergency use The FDA's Vaccines and Related Biological Products Advisory Committee plays a key role in approving flu and other vaccines in the U.S., verifying the shots are safe for public use. While the FDA doesn't have to follow the advisory committee's recommendation, it often does.

After the vote, Dr. Archana Chatterjee, an infectious disease expert at Chicago Medical School and a voting member of the committee, said J&J's vaccine will help "meet the needs of the moment" as states complain there is not enough supply of Pfizer's and Moderna's vaccines.

"We need to get this vaccine out now," Dr. Jay Portnoy, a professor UMKC School of Medicine and a voting member of the committee, said after the vote. He added, "we're in a hurry" as the variants pose a threat to the nation's progress on the pandemic.

No specific safety concerns from J&J's vaccine were identified. Headaches, fatigue and muscle pain were some of the most common side effects among people who received the inoculation, according to an FDA report published Wednesday. There were also reports of nausea, fever and pain at the injection site, the report said.

Macaya Douoguih, head of clinical development and medical affairs for J&J's vaccines division Janssen, told the FDA panel on Friday that two people suffered severe allergic reactions shortly after getting the vaccine. One of the people was participating in an ongoing trial in South Africa and developed anaphylaxis, a severe and life-threatening allergic reaction.

The company has said it plans to ship the vaccine, which contains five doses per vial, at 36 to 46 degrees Fahrenheit. By comparison, Pfizer's vaccine needs to be stored in ultra-cold freezers that keep it between minus 112 and minus 76 degrees Fahrenheit, though the FDA recently allowed the company to store its vaccine for two weeks at temperatures commonly found in pharmaceutical freezers. Moderna's vaccine needs to be shipped at 13 below to 5 degrees above zero Fahrenheit.