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Invasive meningococcal disease (IMD) remains a major cause of morbidity and mortality in children. Post-pandemic epidemiological patterns of pediatric IMD are not well defined in Türkiye. This study aimed to evaluate the epidemiology, clinical characteristics, outcomes, and serogroup distribution of pediatric IMD in a large multicenter cohort in Türkiye, comparing the during-COVID and post-COVID periods. This retrospective multicenter hospital-based study included children aged 1 month-18 years hospitalized with laboratory-confirmed IMD in 39 hospitals across 23 provinces. Cases were grouped as during-COVID (January 2020-May 2022) and post-COVID (June 2022-December 2025). A total of 166 patients (median age 25 months; 59.6% male) were included; 25 occurred during-COVID and 141 post-COVID. The number of reported cases in participating centers increased after 2022, with seasonal peaks in winter and early spring. Children under 5 years accounted for 62.7% of cases, and infants (< 1 year) were the largest single age group overall (38.6%). The proportion of children under 5 years was lower in the post-COVID period (58.9% vs 84.0%; OR 0.27, 95% CI 0.09-0.84), indicating a relative shift toward older age groups rather than a reduction in disease burden among infants. Pediatric intensive care admission occurred in 69.9% of cases, and overall mortality was 13.3%. Mortality varied markedly by clinical form, from 1.2% in meningitis alone to 21.7% in combined meningitis and meningococcemia and 38.1% in meningococcemia alone (p < 0.001). Only 2.4% of children had received any meningococcal vaccine before their illness. Serogroup data were available for 60.8% of patients, with grouping coverage differing between periods (32.0% vs 66.0%). Among cases with available serogroup data, serogroup B accounted for 69.9% in the post-COVID period and for half of the eight grouped cases during the pandemic. In unadjusted exploratory analysis restricted to cases with serogroup data, mortality was higher in serogroup B than non-B infections (21.7% vs 3.1%; OR 8.61, 95% CI 1.08-68.8); in an exploratory model adjusting for clinical form, age, and period, with ungrouped cases retained as a separate category, serogroup B remained associated with mortality (aOR 7.59, 95% CI 1.55-75.65).

In this multicenter hospital-based cohort, reported pediatric IMD cases increased in the post-pandemic period, with a persistent burden in infants, a relative shift toward older age groups, and predominance of serogroup B among grouped cases. These findings highlight the importance of strengthened surveillance and support further evaluation of meningococcal vaccination strategies, including MenB vaccination.

• Invasive meningococcal disease remains a severe pediatric infection with high morbidity and mortality, despite treatment. • The COVID-19 pandemic and the subsequent easing of restrictions altered IMD epidemiology globally.

• Reported pediatric IMD cases increased in the post-pandemic period, with a relative shift toward older children while the proportion of infants remained unchanged (38.3% vs 40.0%); serogroup B predominated among cases with an available serogroup result, although differential availability of these data precludes conclusions about change over time. • Mortality was determined principally by clinical form, ranging from 1.2% in meningitis alone to 38.1% in meningococcemia alone, and only 2.4% of children had received any meningococcal vaccine before their illness.