WHO's Disease Outbreak News 595 reported a recombinant mpox virus (MPXV) carrying genetic elements from both clade Ib and clade IIb1. It was first found in a UK traveller in December 2025 and identified retrospectively in India from September 2025, and now spans at least four countries across three WHO regions2. mpox, formerly monkeypox, circulates in distinct lineages called clades; a recombinant carries DNA from two of them at once.
Recombination happens when two virus lineages co-infect a single host and swap genetic material. It is expected wherever clades circulate together, and detecting it is the reason genomic surveillance exists rather than evidence that surveillance has failed. The strain's appearance on the record is the system working: routine sequencing flagged a hybrid and traced it back through stored samples to September 2025. This is the kind of early signal WHO's R&D Blueprint pathogen-prioritisation programme exists to catch.
WHO calls it premature to draw any conclusion about transmissibility from so few cases, and reports no serious complications in the patients identified3. A hybrid genome does not by itself imply a more dangerous virus, so this reads as a watch item rather than an alarm. Whether the recombinant spreads or sickens differently from its parent strains is a question only more sequencing can answer, and WHO says both sequencing and surveillance are being intensified4.
