EXPLAINER: How will US make more shots available by May 1?

President Joe Biden’s pledge that all U.S. adults will be eligible for coronavirus vaccines by May 1 puts a new challenge in front of the nation. To achieve that goal, the federal government must deliver doses to hundreds of new vaccination sites and recruit more health care workers to administer the shots — all within in the next seven weeks. The government also aims to simplify the often-frustrating sign-up process and to bring shots to communities that are having the hardest time