Resurgent measles in Türkiye: predictors of severe disease in a nationwide paediatric cohort, 2023.

Measles remains among the most important global health threats worldwide. A global increase has been reported since 2022, peaking in 2024, which heightens the risk of imported infections, particularly from unvaccinated children and adults, and measles outbreaks persist where immunity gaps remain. The aim of this study was to assess the clinical severity, complications, and outcomes of measles in hospitalised children as well as the effect of vaccination status on measles in Türkiye in 2023. We performed a retrospective, multicentre cohort study that included 34 medical centres between 1 January and 31 December 2023. Children ≤ 18 years who were hospitalised with WHO-confirmed measles were included. A standard electronic case report form captured demographics, vaccination status, clinical features, complications, and outcomes. Our study outcomes included any major complication, severe disease defined as PICU admission, and in-hospital mortality. We also performed a secondary analysis of the differences in presentation, complications, therapy, and resource use according to vaccination status. A total of 504 children with measles were analysed (median age 26 months, IQR 9-88; 56.3% male). Unvaccinated patients constituted 72.2% (364/504) of the sample; vaccine refusal was documented in 45.9% of this group. Migrants represented 24.6% (124/504) of admissions. The typical symptoms were rash (97.6%), fever (89.5%) and cough (64.5%). Pneumonia (40.3%) was the most common complication. Infants < 9 months, below the age of routine vaccination, made up 27.2% of admissions; 39.4% developed pneumonia, 10.9% required PICU care, and two recorded deaths occurred in this age group. Pneumonia and PICU use were concentrated in the 10-24-month group (pneumonia 45%, PICU 9%). Age-stratified analysis revealed that delayed immunisation compounds risk: Only 1% of toddlers aged 10-24 months had received two measles-containing vaccine doses, and this band registered the highest rates of pneumonia (45.4%), respiratory distress (12.7%) and PICU admission (9.1%). Children who received two or more documented measles vaccine doses had fewer acute otitis media, fewer croup and no PICU admissions (0/18). Overall, 35 patients (6.7%) required a PICU stay, and all three deaths (0.6%) occurred among unvaccinated infants. The median hospital LOS was 6 days (IQR 4-7), irrespective of immunisation status. Conclusion: Measles resurged in Türkiye in 2023 after two quiet pandemic years, fuelled by vaccine hesitancy, underimmunised migrant communities, and vaccine-ineligible infants. Therefore, protecting vaccine-ineligible infants under nine months of age through household catch-up cocooning and prompt clinical management is critical for reducing measles-related morbidity and mortality. This study highlights the critical role of vaccination in preventing severe outcomes of measles. Achieving timely two-dose coverage per the National Immunisation Program could prevent nearly half of pneumonia cases and approximately three-quarters of PICU admissions among vaccine-eligible children in our cohort. Accelerating measles vaccination before the second birthday is critical, and catch-up at any age remains essential because severe measles can occur at any age. What is Known? • Measles outbreaks persist because immunity gaps remain and one of the important global lists health threats in worldwide. • ≥ 95% two-dose measles-containing vaccine coverage is essential for elimination of the disease and herd immunity. What is New? • In this multicentre study in Türkiye, in 2023, every PICU admission and all deaths occurred in children who received < 2 doses; no fully vaccinated patient needed intensive care. • Among the unvaccinated individuals, 40% were migrants, and 64% had documented vaccine refusal, which highlights key targets for catch-up vaccination and risk communication.