Public health officials in England have identified a new recombinant strain of mpox in a traveler recently returned from Asia, prompting renewed calls for vaccination among eligible groups. The UK Health Security Agency (UKHSA) confirmed the case on December 8, 2025, stating that genomic sequencing revealed the virus contains elements of both clade Ib and clade IIb mpox.
This discovery, while not entirely unexpected given the co-circulation of both clades, underscores the virus’s potential for continued evolution and the critical importance of ongoing genomic surveillance, according to the UKHSA. Dr. Katy Sinka, Head of Sexually Transmitted Infections at UKHSA, stated that genomic testing enabled the detection of the new strain and that “it’s normal for viruses to evolve, and further analysis will help us understand more about how mpox is changing.”
Mpox, formerly known as monkeypox, is a viral infection related to the smallpox virus. Symptoms typically begin with fever, headache, muscle aches, and backache, followed by swollen lymph nodes and exhaustion. A rash or sores then develop, often starting on the face and spreading to other parts of the body. Transmission occurs through contact with these sores or fluids, as well as through respiratory secretions during close contact.
Currently, two major clades of the mpox virus are circulating globally: clade IIb and clade Ib. Clade IIb was responsible for the widespread global outbreak in 2022, which infected approximately 114,000 people and caused 220 deaths worldwide. That outbreak was primarily spread through sexual behavior among men who have sex with men and generally caused mild symptoms with a mortality rate of around 1%.
Clade Ib, however, is associated with more severe illness and a fatality rate of approximately 10%. Historically found in the Democratic Republic of Congo (DRC), transmission was largely limited to direct contact with animals. However, a recent outbreak in the DRC, beginning in 2023, has demonstrated person-to-person spread, including transmission within families and healthcare settings due to inadequate protective equipment. Cases have also been reported in children under 15. More recently, sexual transmission of clade Ib has been observed, particularly among sex workers and transient populations.
Between January and November 2025, over 48,000 cases of clade Ib mpox were reported in Central and Eastern Africa. Approximately 43 cases have been identified in other countries, with roughly half linked to recent travel to Africa and the remaining 24 occurring in individuals with no known travel history. The World Health Organization (WHO) has noted local person-to-person spread of clade Ib in Italy, Malaysia, the Netherlands, Portugal, Spain, and the United States.
The newly identified recombinant virus in England combines genetic material from both clade Ib and clade IIb. Experts emphasize that viral recombination is a natural process, but it raises concerns about potential challenges in controlling the virus’s spread. Dr. Boghuma Titanji, assistant professor of medicine at Emory University, told the BBC that the discovery represents a scenario public health officials had feared: “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.”
The UKHSA has shared its findings with international partners, including the WHO, to support global monitoring efforts. The JYNNEOS vaccine, which protects against both mpox and smallpox, is available in the UK for eligible groups, including those with multiple sexual partners, those who participate in group sex, or those who visit sex-on-premises venues. Studies indicate the vaccine is approximately 75% to 80% effective. UKHSA continues to assess the significance of the new strain and urges eligible individuals to get vaccinated.
Anyone suspecting they may have mpox is advised to contact NHS 111 for guidance.
