In December of 2022, Linda Zoslocki, a then-69-year-old retired high school counselor in Modesto, California, had a deep cough that wouldn’t go away. She was tired, and her legs had been swollen for weeks. When her daughter called on a Saturday to see if Zoslocki wanted to come make pizza with her family, her mother told her she wasn’t feeling well and wanted to stay home. Her daughter figured she was struggling with a run-of-the-mill yet stubborn respiratory infection—bronchitis, perhaps.