PHILADELPHIA — The last weekend in January, Krista Xavier did something she described as “tremendously stupid.” She went to an indoor performance at the Met Philadelphia. Xavier, 30, has fibromyalgia and is immunocompromised. She has received two vaccines and a booster shot, but likely isn’t receiving the same benefits from them as someone with a healthy immune system. COVID-19 remains a very real threat to her. She hazards trips, always double masked, to Home Depot to pick up paint supplies, and usually takes some medical marijuana to ease anxiety over COVID-19. Still, she allowed herself tha…