Paediatric mpox during Sierra Leone’s 2024 to 2025 clade IIb outbreak: A national surveillance and outbreak-investigation study of 415 children

BACKGROUND: Evidence on paediatric mpox during contemporary African clade IIb outbreaks remains limited. We described paediatric cases in Sierra Leone's 2024-2025 clade IIb G.1 outbreak by person, time, and place and examined clinical care, outcomes, vaccination records, and documented exposures. METHODOLOGY/PRINCIPAL FINDINGS: We conducted a retrospective descriptive study using the national District Health Information Software 2 (DHIS2) mpox database, supplemented by patient charts and outbreak-investigation forms. Among 5,466 cases with recorded age, 415 (7.6%) were children younger than 15 years; 188 (45.3%) were aged 0-4 years, 121 (29.2%) were aged 5-9 years, and 106 (25.5%) were aged 10-14 years. Of 415 paediatric cases, 411 were laboratory-confirmed. Outcome was recorded for 261 children; three died (1.1%, exact 95% CI 0.2 to 3.3). Care location was recorded for 285 children; 216 (75.8%) received hospital care for isolation, clinical management, or both. Three sporadic paediatric cases of mpox-like illness were reported from 2017 through 2024; notifications then rose rapidly from April 2025 and peaked in May. Western Area Urban accounted for 195/413 cases with known district; crude notified paediatric rates were highest in Western Area Urban, Koinadugu, and Falaba. Household or caregiving contact was the most common documented exposure among 246 classifiable investigation forms (141, 57.3%). Mpox vaccination status was recorded for 27/54 cases aged 12-14 years; six were vaccinated. CONCLUSIONS/SIGNIFICANCE: Children were not spared during Sierra Leone's clade IIb outbreak. Response plans should include children in case finding, contact follow-up, clinical care, and vaccination assessment. DHIS2 should capture epidemiologic links, clinical outcomes, vaccine eligibility and status, and potential exposure settings through standardised fields.