Measles 2025

N Engl J Med . 2025 Dec 18;393(24):2447–2458. doi: 10.1056/NEJMra2504516. Measles remains especially dangerous for young infants and pregnant individuals, 2 populations that face heightened risks during outbreaks. A growing concern is the increasing vulnerability of infants in the first months of life due to the more rapid decline of maternally derived measles antibodies. In both endemic and elimination settings, maternal antibodies now wane earlier than previously observed. Data from multiple countries show that by 3 to 4 months of age, most infants no longer have protective antibody levels, and by 6 months, nearly all are susceptible. This leaves a significant immunity gap before the routinely scheduled first measles vaccine dose in many countries.