Monkeypox Virus Clade IIb Identified in Republic of the Congo

Researchers have identified the presence of monkeypox virus (MPXV) clade IIb lineage A.2.2 in the Republic of the Congo, marking a significant development in the regional circulation of the virus. According to a study published in Nature Medicine on April 3, 2026, this discovery reveals the co-circulation of three distinct clade lineages within the human population, raising concerns regarding the potential for future recombination events.

The findings were established through whole-genome phylogenetic analyses, which confirmed a laboratory-confirmed case of mpox clade IIb lineage A.2.2 in Pointe-Noire, the second largest city in the Republic of the Congo. This specific lineage is currently emerging in West Africa, with a particular presence in Sierra Leone.

Surveillance Data and Co-circulation

Beyond the primary case in Pointe-Noire, passive surveillance conducted in the Republic of the Congo in 2025 identified several other cases of the virus. These findings underscore a complex epidemiological environment where multiple lineages are present simultaneously.

• 16 cases of clade Ia were identified.
• 32 cases of clade Ib were identified.
• One additional introduction of clade IIb was recorded.

The detection of clade IIb marks the third distinct MPXV clade and lineage co-circulating in the human population of the region, appearing alongside clade Ia and clade Ib.

Historical Distribution and Viral Shifts

Historically, the distribution of monkeypox virus clades was divided primarily by region. Clade I MPXV circulation was typically observed in the Democratic Republic of the Congo, the Republic of the Congo, the Central African Republic, South Sudan, Gabon and Cameroon.

In contrast, clade II circulation was historically observed in West African nations, including Sierra Leone, Liberia, Ivory Coast, Ghana, Benin, Cameroon, and Nigeria.

The emergence of clade IIb gained global attention in 2022, when it caused a global epidemic. That outbreak was driven by human-to-human transmission, occurring mostly through sexual contact, primarily among the population of men who have sex with men.

Public Health Implications and Risks

The co-circulation of clade Ia, Ib, and IIb in the Republic of the Congo emphasizes the urgent need for enhanced public health strategies. Scientists have noted that the presence of multiple lineages increases the risk of possible recombination events in the future, which could potentially alter the characteristics of the virus.

To mitigate these risks, the study highlights several critical requirements for the region and the global health community:

• Improved surveillance and diagnostic strategies to accurately identify which clade and lineage are circulating in the human population.
• Strengthened regional capacity for case detection and contact-tracing.
• Implementation of robust public health measures.
• Access to affordable vaccines to reduce the global risk associated with both clade I and clade II MPXV.

The scientific community continues to study the differences in virulence between these clades. Research published in Communications Biology indicates an enhanced virulence of mpox virus clade Ib over clade IIb when tested in the CAST/EiJ mouse model.

The discovery of lineage A.2.2 in the Republic of the Congo suggests that the geographic boundaries previously associated with these clades are shifting, necessitating a more dynamic and integrated approach to viral monitoring in Central and West Africa.