WHO confirmed that two cases of the recombinant strain – combining genomic elements of clades Ib and IIb of the monkeypox virus (MPXV) – have been identified to date: one in the United Kingdom and one in India. Both patients had recent travel histories, and neither experienced severe illness.

No secondary cases were detected following contact tracing.

WHO has published a detailed update on the two cases and the national responses.

Recombination is a natural process that can occur when two related viruses infect the same person and exchange genetic material, producing a new variant.

According to WHO, detailed genomic analysis shows the two individuals “fell ill several weeks apart with the same recombinant strain,” suggesting that additional undetected cases may exist.

Two detected cases

The case in the United Kingdom was detected in December 2025 in a traveller returning from a country in the Asia Pacific region. Initial laboratory testing identified the virus as clade Ib, but whole genome sequencing later revealed that it contained genetic regions from both clade Ib and clade IIb strains. Repeat sequencing confirmed the findings and demonstrated that the virus “can replicate and presents potential for onward transmission.”

In India, a patient who developed symptoms in September 2025 was initially classified as infected with clade II MPXV. However, following updates to global genomic databases, the virus was reclassified as the same recombinant strain identified in the UK. The Indian case represents the earliest known detection of this strain.

“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,” WHO said.

Clinical presentations in both cases were consistent with known mpox infections.

Risk assessment unchanged

WHO’s overall risk assessment 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.

At the same time, WHO cautioned that clade differentiation PCR tests alone “may not reliably identify recombinant MPXV strains,” meaning genomic sequencing is essential for detection.

“All countries should remain alert to the possibility of MPXV genetic recombination,” WHO said, urging continued epidemiological surveillance, sequencing, vaccination of at-risk groups, and infection prevention and control measures.

WHO advised that no travel or trade restrictions are warranted based on current information.