Mpox clade Ib
Clade I mpox lineage first identified in eastern DR Congo in 2023.
clade Ib's biggest outbreak is now in Madagascar, where WHO counted 3,436 confirmed cases and 22 deaths by 16 August 2026, a year after Europe recorded its first locally acquired infections with the lineage.
Last refreshed: 4 October 2026 · Appears in 1 active topic
How is mpox clade Ib different from the 2022 outbreak strain, and does the vaccine still work?
Timeline for Mpox clade Ib
Caused all 3,436 confirmed Madagascar cases
Pandemics and Biosecurity: Madagascar logs half July's mpox casesConfirmed circulating locally in Europe among MSM with no Africa travel history
Pandemics and Biosecurity: Mpox clade Ib now spreads in EuropeBackground
clade Ib is a lineage of clade I mpox, first identified in eastern DR Congo in 2023. Clade I is the branch historically linked to more severe disease than clade IIb, the virus behind the 2022 global outbreak. clade Ib spreads through household and close contact as well as sex, so it is not confined to the sexual networks that carried the 2022 virus.
ECDC reported Europe's first locally acquired cases in October 2025: Spain on 10 October, then four more in Italy, Portugal and the Netherlands on 17 October, all in men with no travel history. ECDC rated the risk moderate for men who have sex with men and low for the general public. A recombinant virus carrying clade Ib and clade IIb genes was reported in May 2026.
The emergency footing around it has eased. WHO ended the mpox Public Health Emergency of International Concern on 5 September 2025, and Africa CDC lifted its continental emergency in January 2026. WHO has extended its standing mpox recommendations under the International Health Regulations to August 2027, and on 27 August 2026 a standing mpox vaccine reserve opened, with UNICEF buying the doses and Gavi paying for them.
Clade Ib has found a new front
The lineage now spreads on two different patterns. In Europe it has circulated locally among men who have sex with men since October 2025, and in June 2026 that spread was continuing, while all 23 confirmed US clade I cases were travel-linked.
Madagascar shows the other pattern. Every one of the island's 3,436 confirmed cases to 16 August was clade Ib, and they ran across all ages and both sexes, the general-population spread seen in central Africa rather than Europe's network spread. WHO's September report read 67% test positivity as a sign that surveillance misses many infections. The lineage also kept reaching new countries: Chile and Hungary reported their first clade Ib cases in the same report.
What is mpox clade Ib and how is it different from the 2022 mpox outbreak?
Has mpox clade Ib spread in Europe?
Where is the largest mpox clade Ib outbreak?
Is mpox still a global health emergency?
Written with AI from Lowdown's published reporting. Not individually reviewed by an editor. Updated 4 October 2026. Editorial standards.