(CNN)The US Food and Drug Administration on Wednesday authorized Novavax's Covid-19 vaccine for emergency use in adults. It is the fourth coronavirus vaccine available in the United States, and it uses a different type of vaccine technology than the shots already available. Novavax's vaccine will be available as two-dose primary series for people 18 and older. The FDA's independent Vaccines and Related Biological Products Advisory Committee voted in favor of authorization of the vaccine June 7, saying that the benefits of the vaccine outweigh its risks for adults. It is also being used in 170 other countries.