(CNN) -
The United States Food and Drug Administration has authorized Moderna's covid-19 vaccine for emergency use in that country.
The FDA made its announcement on Twitter late Friday, following the recommendation of its Advisory Commission on Vaccines and Related Biologics on Thursday.
"The emergency use authorization allows the vaccine to be distributed in the United States for use in people 18 years of age and older," the FDA said in its tweet.
Last weekend, the FDA cleared Pfizer's vaccine, whose two-dose regimen is 95% effective in people 16 years of age and older.
Pfizer and Moderna vaccines against covid-19: what are their similarities and differences?
Does Moderna's vaccine work?
The Moderna vaccine was effective in preventing COVID-19 cases in total and limiting severe COVID-19 during the testing phase.
The efficacy of the COVID-19 vaccine was 94.1%, and it occurred at least 14 days after the second dose, according to an information paper released by an FDA advisory committee.
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In Moderna's trial, 15,000 study participants received a placebo, which is a saline injection that has no effect.
Over several months, 185 of them developed covid-19, and 30 developed severe forms of the disease.
One of them died.
Another 15,000 participants were given the vaccine and only 11 of them developed COVID-19.
None of the 11 became seriously ill.
The vaccine was effective in all age groups, genders, races and ethnic groups, and participants with medical comorbidities associated with a high risk of severe COVID-19, according to the information document.
About 10% of the study participants were black, and 20% were Hispanic or Latino.
How does Moderna's vaccine work?
Like the Pfizer vaccine, Moderna offers messenger RNA, or mRNA, which is a genetic recipe for making some of the spikes found on coronavirus.
Once injected, the body's immune system produces antibodies against the spikes.
If a vaccinated person is later exposed to the coronavirus, those antibodies must be ready to attack the virus.
The Moderna vaccine in particular contains a synthetic mRNA that encodes a structure called the "pre-fusion stabilized peak glycoprotein" of the virus.
The vaccine also contains fatty materials called lipids, tromethamine, tromethamine hydrochloride, acetic acid, sodium acetate, and sucrose.
With information from Amanda Watts, Eric Levenson and Jacqueline Howard
FDA Modern