Mpox Multi-country external situation report no. 62
#19,055
Although details were scant, on December 8th, 2025 the UKHSA Identified a New Recombinant Strain of Mpox Virus in a traveler recently returning from an (undisclosed) country in South-East Asia.
For the very first time, genomic sequencing showed this mpox genome contained elements of clade Ib and IIb mpox.While a new development, we've seen warnings for more than a decade on the potential for Mpox to mutate (see 2014's Genomic Variability of Monkeypox Virus among Humans, Democratic Republic of the Congo).
Two days later we looked at academic reactions to this announcement (see The UK Recombinant Mpox Case: Reactions from the UK Science Media Centre), which included the following:
Dr Boghuma Titanji, Assistant Professor of Medicine, Emory University, said:
“The identification of a recombinant mpox strain containing elements of both Clade I and Clade II is precisely what experts in the field feared would happen if the virus continued to spread globally without a decisive response to stop it.
Orthopoxviruses are well known for their ability to exchange portions of their genome and recombine to generate new variants, this is a core mechanism of their evolution. The key concern now is whether events like this will alter the virus’s transmissibility or virulence. There are also implications for how well existing testing platforms can identify these emerging recombinant strains.
The more mpox circulation we permit, the more opportunities the virus has to recombine and adapt, further entrenching mpox virus as a human pathogen that is not going away.”
Since then, a second (albeit, earlier) case has been identified, which was reported by India in a resident with recent travel to another (undisclosed) country on the Arabian Peninsula.
Despite originating from two different regions of the world, Whole‑genome sequencing (WGS) showed >99.9% similarity between the two viruses.
While routine PCR tests can identify these cases as Mpox, it requires full WSG to identify correctly flag them as being a `mixed-strain' virus; tests that are generally only run in a minority of cases, and mostly by high-income nations.
Leaving us with an uncomfortably large knowledge gap at this point.
I've reproduced several excerpts from the WHO DON report below. Follow the link to read it in its entirety. I'll have a bit more after the break.
Mpox: recombinant virus with genomic elements of clades Ib and IIb - Global
14 February 2026
Situation at a glance
Recombination of monkeypox virus (MPXV) strains has been documented in recent months, with two cases of a recombinant strain comprising clade Ib and IIb MPXV reported. Recombination is a known natural process that can occur when two related viruses infecting the same individual exchange genetic material, producing a new virus.
The first case was detected in the United Kingdom of Great Britain and Northern Ireland (hereafter “United Kingdom”), with travel history to a country in South-East Asia, and the second in India, with travel history to a country in the Arabian Peninsula.Detailed analysis of the virus genomes shows that the two individuals fell ill several weeks apart with the same recombinant strain, suggesting that there may be further cases than are currently reported. Both cases had similar clinical presentation to that observed for other clades. Neither patient experienced severe outcomes. Contact tracing for both cases in the reporting countries has been completed; no secondary cases were detected.Based on available information, the overall WHO public health risk assessment for mpox remains unchanged: the risk is assessed as moderate for men who have sex with men with new and/or multiple partners and for sex workers or others with multiple casual sexual partners, and low for the general population without specific risk factors.
Description of the situation
In December 2025, the United Kingdom detected the first reported case of a clade Ib/IIb MPXV recombinant strain.5 After classification of this case and posting in a public database as a novel MPXV recombinant strain, a case of mpox detected in India in September 2025 was retrospectively reclassified as a closely-related recombinant strain based on sequencing data. To date, these are the only known cases of this recombinant virus.
Case detected in the United Kingdom of Great Britain and Northern Ireland
The case was identified following testing of a vesicular swab from a traveler who had returned from a country in the Asia Pacific region in October 2025. During laboratory confirmation, the virus was initially typed as clade Ib MPXV by qPCR. Subsequent whole genome sequencing revealed that the MPXV strain identified was distinct from other known clade Ib MPXV strains with phylogenetic analysis indicating that the genome had regions similar to both clade Ib and clade IIb MPXV reference sequences, suggesting that it is an inter-clade recombinant.To confirm this unusual finding, sequencing was repeated on the original extract from the primary sample, a fresh extract from the same primary sample, a second swab collected from the patient at the same time, and a cultured isolate derived from the initial swab. This repeat sequencing yielded identical viral genome sequences from the two clinical swabs and the cultured isolate, supporting the initial findings of a new recombinant strain, and showing that it can replicate and presents potential for onward transmission.This strain is a recombinant MPXV, containing genetic elements from both clade Ib and clade IIb MPXV. A small number of contacts were identified and followed up in the United Kingdom; none developed any clinical features of mpox. Health worker contacts had worn full personal protective equipment (PPE) during provision of medical care to the patient. The authorities of the United Kingdom continue to investigate the significance of this recombinant MPXV strain through phenotypic characterization studies.
Case detected in India
On 13 January 2026, the National IHR Focal Point (NFP) of India notified WHO of a mpox case with an inter‑clade recombinant MPXV which was, upon whole-genome sequencing, found to have genomic elements of clades Ib and IIb MPXV.
The recombinant virus was found in samples from a man with mpox who had presented for care in September 2025. The patient had reported recent travel from a country in the Arabian Peninsula, where he resides as an overseas worker.
He developed symptoms on 1 September 2025, while still abroad. After his return to India, real‑time PCR confirmed MPXV infection on 11 September 2025. Clade differentiation PCR performed on 15 September 2025 initially identified this virus as clade II MPXV. Initial genomic sequencing analysis suggested features consistent with clade IIb MPXV. However, following the update of the global Nextclade database on 16 December 2025, which included the recombinant clade Ib/IIb MPXV strain reported by the United Kingdom, the virus from the patient in India was reclassified as belonging to the recombinant strain. Recombination analysis demonstrated mosaic patterns containing genomic regions derived from both parent clades.
Following the initial diagnosis, the patient was hospitalized, did not experience any medical complications, and fully recovered, testing negative for MPXV on 29 September 2025. The case reported no close contacts in India, and no known secondary cases were identified following this introduction of the recombinant clade Ib/IIb MPXV in India.
Full or near‑full genome retrieval (>99%) from both the sample and a sample-derived virus isolate enabled phylogenetic analysis showing >99.9% similarity to the recombinant strain detected in the United Kingdom. A total of 34 recombinant tracts were observed in the sequence reported by India, while 28 recombinant tracts were observed in the sequence reported by the United Kingdom; 16 recombinant tracts were common to both strains. This case in India therefore represents the earliest known detection of this recombinant strain globally, having preceded the event reported in the United Kingdom.
Consistent with the case reported in the United Kingdom, clinical presentation was consistent with cases due to clade I or clade II MPXV (non-recombinant MPXV) infection.
(SNIP)
WHO risk assessment
Mpox outbreaks must be considered in their local context, with meaningful involvement of affected communities, to ensure an in-depth understanding of the epidemiology, modes of transmission, risk factors for severe disease, viral reservoir and evolution, and relevance of strategic approaches and countermeasures for prevention and control.
Multiple strains of MPXV are circulating through interconnected sexual networks across many countries and settings. Co-infection with different strains, that could lead to emergence of recombinant virus strains, while rare, can be expected. The case in India was infected with the same recombinant Ib/IIb MPXV strain detected in the United Kingdom. Symptom onset in the case reported in India occurred more than two months earlier than the case in the United Kingdom, and the great degree of similarity between their sequences suggests a common evolutionary history. This information has two important implications: i) the origin of the recombinant strain remains unknown; and ii) transmission of this recombinant virus already involves at least four countries in three WHO regions, and is therefore likely to be more widespread than currently documented.
For the cases in the United Kingdom and India, the initial clade differentiation PCR results indicated clade Ib and IIb MPXV, respectively. Thus, clade differentiation PCR assays alone may not reliably identify recombinant MPXV strains, and genomic sequencing is likely to be required for their detection.
Due to the small number of cases found to date, conclusions about transmissibility or clinical characterization of mpox due to recombinant strains would be premature, and it remains essential to maintain vigilance regarding this development.
In light of the limited information available on this recombinant MPXV strain, the overall WHO public health risk assessment for mpox remains unchanged: the risk is assessed as moderate for men who have sex with men with new and/or multiple partners and for sex workers or others with multiple casual sexual partners, and low for the general population without specific risk factors.
All countries should remain alert to the possibility of MPXV genetic recombination. The public health risk posed by any newly detected recombinant strain should be assessed on a case-by-case basis, considering available epidemiological, clinical and genomic information.
Increasingly over the past few years we've entered the age of the `redacted' epidemiological report (see last December's ECDC Epidemiological Update: 2 Imported MERS-CoV Cases In France), where key details are sometimes omitted in order to encourage countries to report without fear of stigma or economic/political fallout.
While disappointing, it is probably safe to assume this recombinant has already spread beyond the borders of the two undisclosed countries.
With only limited data, the WHO appears to be taking a conservative, but cautious, approach. For now, their risk assessment remains unchanged, but they urge member nations to expand WGS in order to detect hidden spread of this emerging strain.
Sound advice, since this is unlikely to be the last evolutionary leap that Mpox makes.
