The nearly 1 million people around the world who have lost their lives to COVID-19 have left us a gift: Through desperate efforts to save their lives, scientists now better understand how to treat and prevent the disease — and millions of others may survive.

Ming Wang, 71, and his wife were on a cruise from Australia, taking a break after decades of running the family's Chinese restaurant in Papillion, Nebraska, when he was infected. In the 74 days he was hospitalized before his death in June, doctors frantically tried various experimental approaches, including enrolling him in a study of an a...