New Mpox Strain Identified in England: Combining Two Virus Types

Public health officials in the United Kingdom have identified a new, combined type of mpox in a traveler recently returned from Asia. This discovery, announced in December 2025, signals a potential shift in the evolving landscape of the virus and raises concerns about future transmission. While details about the individual patient remain confidential, genomic testing reveals the virus is a unique recombination of previously known mpox clades, prompting further investigation by health authorities.

Understanding Mpox and Its Variants

Mpox, formerly known as monkeypox, is a viral infection related to the smallpox virus. Initial symptoms often include fever, headache, muscle aches, and backache, accompanied by swollen lymph nodes and general exhaustion. Typically, a rash or sores develop a few days after these initial symptoms, often starting on the face and spreading to other parts of the body. Transmission occurs through direct contact with these sores, or with materials – like clothing or bedding – that have come into contact with the virus. The virus can also spread through respiratory secretions, such as those produced during kissing or close conversation. More information about mpox and sexual health is available from ASHA.

Currently, researchers have identified two main circulating clades of the mpox virus: Clade IIb and Clade Ib. These clades differ in their severity and transmission patterns.

Clade IIb: The 2022 Outbreak

Clade IIb was responsible for the global mpox outbreak in 2022, which infected approximately 114,000 people and caused 220 deaths worldwide. The United States experienced a peak of around 11,000 cases per month during the summer of 2022. This clade is known for person-to-person transmission, particularly through sexual contact among men who have sex with men. Generally, Clade IIb causes milder symptoms and has a relatively low mortality rate of around 1%.

Clade Ib: A More Severe Threat

Clade Ib, in contrast, is associated with more severe illness and a higher fatality rate, estimated at around 10%. This variant has been present in the Democratic Republic of Congo (DRC) for years, primarily spreading from animals to humans through activities like butchering and consuming bushmeat. But, a recent outbreak that began in the DRC in 2023 has demonstrated person-to-person transmission. In some regions of Africa, transmission is occurring within families through everyday household activities and in healthcare settings due to inadequate protective equipment, with a disproportionate number of cases reported in children under 15. Sexual transmission of Clade Ib is also emerging, with many cases observed 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) now believes Clade Ib is spreading locally in several countries, including Italy, Malaysia, the Netherlands, Portugal, Spain, and the United States.

A Recombinant Virus: Combining Clade IIb and Clade Ib

The recent case identified in England presents a novel situation: genomic tests have revealed a virus containing elements of both Clade IIb and Clade Ib. This is termed a recombinant virus, formed when two related viruses exchange genetic material while infecting the same individual. Experts acknowledge that viral recombination is a natural process, particularly when multiple variants are circulating simultaneously. Further details on the initial detection in England are available from Virological.

The primary concern surrounding this recombinant strain is its potential to complicate efforts to control the spread of mpox. As Dr. Boghuma Titanji, assistant professor of medicine at Emory University, told the BBC, “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.” This highlights the importance of ongoing surveillance and preventative measures.

Vaccination and Prevention

Fortunately, a vaccine, JYNNEOS, is available to protect against both mpox and smallpox. The vaccine is administered in two doses, four weeks apart, and significantly reduces the risk of infection and severe illness.

The Centers for Disease Control and Prevention (CDC) recommends the mpox vaccine for specific groups, including gay, bisexual, transgender, or other men who have sex with men who have had or anticipate having one or more sexually transmitted infections, multiple sexual partners, anonymous sexual encounters, or participation in group sex or visits to commercial sex venues. This targeted vaccination campaign played a crucial role in curbing the spread of mpox in the United States in 2022.

Individuals who meet these criteria and have not yet been vaccinated are encouraged to do so promptly. While the new recombinant type of mpox has not yet been detected in the United States, both Clade IIb and Clade Ib continue to circulate at low levels. The WHO provides ongoing updates on the global mpox situation.

Public health officials are continuing to monitor the situation closely, conducting genomic surveillance to track the spread of the recombinant virus and assess its potential impact. Further research is needed to understand the characteristics of this new strain, including its transmissibility, severity, and response to existing vaccines and treatments. The ongoing process of genomic sequencing and data sharing will be critical in informing public health strategies and mitigating the risk of future outbreaks.