The United States will know by the end of the year or the beginning of 2021 whether a coronavirus vaccine is safe and effective, Dr. Anthony Fauci, the nation's leading infectious diseases doctor, said Monday. Multiple vaccine candidates are being studied, and "if things go the way it looks like they're going, one of these will enter phase 3 at the end of July," he said, referring to the final phase of clinical trials needed to determine whether a drug works. Other vaccine candidates will enter phase 3 trials after July, and "we hope that by end of this year, or the beginning of 2021 we will at least have an answer whether the vaccine or vaccines - plural - are safe and effective," Fauci said.