Measles Seroprotection and Catch-Up Vaccination in Medical Students and Other Healthcare Workers at a Large Teaching Hospital: Positive Impact of Mandatory Italian Vaccination Policies.

BACKGROUND: Measles resurgence across Europe has renewed attention to immunity gaps in healthcare environments. Following decades of sub-optimal coverage, Italy implemented mandatory vaccination under Law 119/2017 to counteract declining rates. However, young adults entering medical training represent a transitional cohort with heterogeneous exposures to natural infection versus vaccination. This study evaluated the evolution of measles immunity among medical students and healthcare trainees, assessing the impact of vaccination policies and the operational efficacy of an on-site catch-up vaccination pathway. METHODS: We conducted an observational study of 1014 medical-area students and young healthcare workers aged 18-35 years undergoing occupational surveillance in 2025 at Policlinico Tor Vergata, Rome. Measles IgG antibodies were quantified by chemiluminescent immunoassay (VIRCLIA® S/CO > 1.0 defining protection). Findings were compared with baseline institutional data from 2020. RESULTS: Overall seroprotection in 2025 was 91.8% (931/1014). Stratification showed no significant differences by sex (92.6% female vs. 90.1% male; p = 0.168), age group (92.8% in 18-25 vs. 90.9% in 26-35 years; p = 0.249), or nationality. Among the 83 sub-threshold individuals, 42.2% had documented prior immunization, reflecting secondary humoral waning rather than primary vaccine failure. On-site revaccination raised final seroprotection to 95.4%. Comparative assessment demonstrated a significant progressive shift from natural wild-type exposure toward vaccine-induced immunity over the past decade. CONCLUSIONS: Mandatory vaccination policies have stabilized baseline protection, yet waning humoral titers among vaccinated young adults present unique operational challenges. A structured occupational protocol combining serological screening, historical verification, and on-site revaccination effectively closes nosocomial immunity gaps.