A few hours after getting the second dose of her COVID-19 vaccine one morning in mid-February, Wendy Reiter's arm was a bit sore, just as it was after her first shot. But by evening, she felt flu-like, with body aches, a headache and serious fatigue. “I felt like I was hit by a truck. I was essentially laid up for a day and a half, sleeping on an off all day and feeling out of it,” Reiter, 75, an …