Children were 1 in 13 mpox cases in Sierra Leone's clade IIb outbreak, data show

Children were not spared in Sierra Leone's 2024–2025 mpox outbreak. A national surveillance and outbreak-investigation study, published in PLOS Neglected Tropical Diseases on 7 October 2026, found that of 5,466 cases with a recorded age, 415 — about one in 13, or 7.6% — were children younger than 15 [s1]. The finding cuts against an early assumption of the clade IIb epidemic in West Africa, which spread largely through adult contact networks, that young children would be peripheral to it.

What was done

The study is a retrospective descriptive analysis rather than a trial. Researchers drew on Sierra Leone's national District Health Information Software 2 (DHIS2) mpox database, supplemented by patient charts and outbreak-investigation forms, to characterise paediatric cases by person, time and place, and to examine their clinical care, outcomes, vaccination records and documented exposures [s1]. The outbreak was caused by clade IIb lineage G.1 — the same clade behind the global 2022 spread, distinct from the clade I viruses driving the larger epidemic in the Democratic Republic of the Congo.

Who the children were

Among the 415 paediatric cases, the youngest band was the largest: 188 children (45.3%) were aged 0–4 years, 121 (29.2%) were 5–9, and 106 (25.5%) were 10–14 [s1]. Diagnosis was rarely in doubt — 411 of the 415 were laboratory-confirmed [s1].

The epidemic curve was steep. Only three sporadic paediatric cases of mpox-like illness had been reported across the seven years from 2017 through 2024; notifications then rose rapidly from April 2025 and peaked in May [s1]. That shape — years of near-silence, then a sudden climb — is the signature of a pathogen finding a new transmission route rather than a long-smouldering endemic presence.

Where, and how, children caught it

The outbreak was concentrated in the capital region. Western Area Urban, which contains Freetown, accounted for 195 of the 413 paediatric cases with a known district, and crude notified paediatric rates were highest there and in the northern districts of Koinadugu and Falaba [s1].

The exposure data point to the home. Among 246 investigation forms that could be classified, household or caregiving contact was the single most common documented exposure, recorded for 141 children (57.3%) [s1]. For a disease often framed around adult networks, that places a substantial share of paediatric transmission inside families — where an infected parent or carer passes it to a child through ordinary close contact.

Outcomes and care

Outcomes were recorded for 261 of the children, among whom three died — a case-fatality of 1.1% (exact 95% CI 0.2 to 3.3) [s1]. The illness was serious enough to pull most affected children into facilities: of 285 with a recorded care location, 216 (75.8%) received hospital care, for isolation, clinical management, or both [s1]. In a crowded urban outbreak, that reliance on hospital isolation is also a demand on a health system already stretched by the adult caseload.

Vaccination data were thin. Mpox vaccination status was recorded for only 27 of 54 cases aged 12–14 — the band old enough to be eligible under some protocols — and of those, six were vaccinated [s1]. The gaps in that field are part of the study's point.

The caveats

This is surveillance data, with the limits that implies. It is retrospective and descriptive, drawn from an operational database rather than a research cohort, so denominators shift from measure to measure — outcomes were known for 261 children, care location for 285, exposure for 246 — and missing fields are common. A case-fatality estimate built on 261 records with three deaths carries a wide confidence interval, as the authors' 0.2–3.3% range makes plain. The figures describe what the system captured, not necessarily the full paediatric burden.

Why it matters

The authors' conclusion is operational: response plans should include children in case finding, contact follow-up, clinical care and vaccination assessment, and surveillance systems like DHIS2 should be built to capture epidemiologic links, clinical outcomes, vaccine eligibility and exposure settings through standardised fields [s1]. The thin vaccination records and inconsistent denominators in this dataset are themselves the argument — you cannot protect a group you are not systematically counting. For the next clade IIb outbreak in the region, the lesson is that children are part of the picture from the start.