One day in March of 2020, Rosemary Bily suddenly grew so tired she could barely get out of bed. “She slept a lot,” said her son-in-law Rich Lamanno. “She was wiped out for most of a month.” Ms. Bily, now 86, also developed nausea and diarrhea, along with a slight cough, and subsisted mostly on Tylenol and Gatorade.