A measles, mumps, and rubella vaccine is prepared at Seminole Hospital District in Seminole, Texas, Feb. 24, 2025. In South Carolina, parents struggle to deal with infections that have brought quarantines and remote learning as health workers are bracing for an increase in cases. (Desiree Rios/The New York Times) By EDUARDO MEDINA and NICK MADIGAN Late-night emails sent to parents informing them that someone in their child’s classroom has been infected with measles. Pediatricians fielding...