The Food and Drug Administration said the shot should only be given to adults who cannot receive a different vaccine or specifically request J&J's vaccine. U.S. authorities for months have recommended that Americans starting their COVID-19 vaccinations use the Pfizer or Moderna shots instead. FDA officials said in a statement that they decided to restrict J&J's vaccine after taking another look at data on the risk of life-threatening blood clots within two weeks of vaccination. J&J's vaccine was initially considered an important tool in fighting the pandemic because it required only one shot. But the single-dose option proved less effective...