New Mpox Strain Identified in England: What You Need to Know
Public health officials in England have identified a new variant of mpox in a traveler recently returned from Asia. Genomic sequencing revealed the virus is a recombination of the two known clades, IIb and Ib, raising concerns about potential implications for future spread.
Understanding Mpox
Mpox is a virus related to the smallpox virus. Initial symptoms typically include fever, headache, muscle aches, and backache, often accompanied by swollen lymph nodes and exhaustion. Within a few days, a rash or sores may develop, initially appearing on the face and then spreading to other parts of the body.
The virus spreads through direct contact with sores or fluids from those sores, even if present on items like clothing or bedding. Transmission can also occur via saliva and respiratory droplets, meaning close contact, such as kissing, can facilitate infection.
Two Current Clades
Researchers have identified two main types of mpox currently circulating globally: Clade IIb and Clade Ib.
Clade IIb Mpox
Clade IIb was responsible for the widespread outbreak in 2022, infecting 114,000 people and causing 220 deaths worldwide. In the United States, the outbreak peaked in the summer of 2022, with approximately 11,000 cases reported each month.
This clade is known for person-to-person transmission, particularly through sexual behavior among men who have sex with men. Clade IIb generally causes milder symptoms and has a mortality rate of around 1%.
Clade Ib Mpox
Clade Ib causes more severe illness, with a fatality rate of approximately 10%. Historically found in the Democratic Republic of Congo (DRC), transmission was primarily from animals to humans through activities like butchering and consumption. However, a new outbreak beginning in the DRC in 2023 is demonstrating person-to-person spread.
In some African regions, Clade Ib is spreading within families through daily household activities and in healthcare settings where protective gear is lacking. Cases, including those in children under 15, are being reported. Sexual transmission, including heterosexual transmission among sex workers and transient workers, is also occurring—a first for this clade.
Between January and November 2025, over 48,000 cases of Clade Ib mpox were reported in Central and Eastern Africa, with about 43 cases identified in other countries. Of those, roughly half involved recent travel to Africa, while 24 cases were found in individuals with no recent travel history.
The World Health Organization reports that Clade Ib mpox is now spreading locally in Italy, Malaysia, the Netherlands, Portugal, Spain, and the United States.
A Recombinant Virus Emerges
Testing revealed the virus identified in England combines genetic material from both Clade IIb and Clade Ib, creating a recombinant virus. Experts note that viral recombination is a natural evolutionary process, especially when multiple variants are circulating simultaneously.
The concern, as stated by Dr. Boghuma Titanji, assistant professor of medicine at Emory University, is that increased circulation of mpox allows for more opportunities for the virus to recombine and adapt, potentially establishing mpox as a persistent human pathogen.
Vaccination Remains Key
The JYNNEOS vaccine offers protection against both mpox and smallpox. Administered in two doses, four weeks apart, vaccination reduces the risk of infection and spread, and can lessen symptom severity if infection occurs.
The Centers for Disease Control and Prevention (CDC) recommends the vaccine for 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 or intimate contact, sex at a commercial sex venue, or sex in association with a large public event in an area experiencing mpox transmission.
A vaccination campaign targeting these groups contributed to halting the spread of mpox in the United States in 2022. Individuals meeting these criteria who have not yet been vaccinated are encouraged to do so, as both Clade IIb and Clade Ib continue to circulate in the U.S. at low levels.
Frequently Asked Questions
What are the first symptoms of mpox?
The first symptoms of mpox are usually fever, headache, muscle aches, and backache. These may be followed by swollen lymph nodes and exhaustion, and then a rash or sores that appear on the face and spread to other parts of the body.
What is the difference between Clade IIb and Clade Ib mpox?
Clade IIb mpox caused the 2022 global outbreak and generally causes milder symptoms with a 1% mortality rate. Clade Ib mpox causes more serious illness with a fatality rate around 10% and has been spreading person-to-person in Africa.
Who is recommended to get the mpox vaccine?
The CDC recommends the mpox vaccine to gay, bisexual, transgender, or other men who have sex with men who have had or expect to have one or more sexually transmitted infections, multiple sexual partners, anonymous sexual or intimate contact, sex at a commercial sex venue, or sex in association with a large public event in a geographic area where mpox transmission is occurring.
Given the emergence of this new recombinant strain, what proactive steps can individuals take to protect themselves and their communities?