Older people are less likely to be diagnosed but more likely to experience certain kinds of illnesses, research suggests.

Ask Patricia Anderson how she is doing, and you probably will not get a routine answer. “Today, I’m working and I’m fine,” she said on a recent Tuesday. “Saturday and Sunday, I was bedridden. Long Covid is a roller coaster.”

Before the pandemic, Ms. Anderson practiced martial arts and did without a car, instead walking and taking buses around Ann Arbor, Mich., where she is a medical librarian. Just before contracting Covid-19 in March 2020, she had racked up — oh, she keeps track — 11,409 steps in one day.