Sierra Leone Mpox Outbreak: Clade IIb Report

The current mpox outbreak in Sierra Leone is the largest ever recorded in the country and the first major epidemic caused by the clade IIb monkeypox virus in Africa. Since a public health emergency was declared on Jan 13, 2025,1 3682 confirmed cases have been reported in Sierra Leone (as of June 4, 2025), with 2225 (60·4%) cases in Freetown (western urban), 748 (20·3%) cases in nearby suburban towns (western rural), and 709 (19·3%) cases distributed across the 14 other districts. Case numbers remained low throughout mid-April, but surged in late April (week 17) and throughout May, exceeding 600 confirmed cases weekly and indicating sustained transmission despite early signs of stabilisation (unpublished data).