On the morning of Dec. 16, the threat of a Virginia snowstorm canceled school for 7-year-old Alain Bell. He instead spent the morning scribbling a scowling face in black marker onto his father’s newly vaccinated upper arm. “It was his idea,” Alain said over Zoom, pointing to his father, Dr. Taison Bell, 37, a critical care physician at UVA Health in Charlottesville. “I feel good that he’s not going to get sick.”