U.S. health officials have allowed emergency use of a second antibody drug to help the immune system fight COVID-19. It’s an experimental medicine that President Donald Trump was given when he was sickened last month. The Food and Drug Administration on Saturday authorized use of the Regeneron Pharmaceuticals Inc. drug for people with mild-to-moderate symptoms. Tests of the drug are continuing, but early results suggest it may prevent hospitalization and emergency room visits. Use is allowed for adults and children 12 and over who are at high risk of severe illness from COVID-19 because of age or certain other medical conditions.