The United States on Saturday authorized Johnson & Johnson's Covid vaccine for emergency use, giving the nation a third shot to battle the outbreak that has killed more than 500,000 Americans. "The authorization of this vaccine expands the availability of vaccines, the best medical prevention method for Covid-19, to help us in the fight against this pandemic, which has claimed over half a million lives in the United States," said acting Food and Drug Administration director Janet Woodcock. jm/bfm