Despite the World Health Institution lifting its global health emergency declaration in September 2025, mpox remains a public health concern as the virus continues to evolve and spread, with recent cases reported in the United States and globally [[1]], [[2]]. Health officials in the United Kingdom have now identified a novel recombinant strain of mpox,a rare occurrence signaling ongoing genetic shifts within the virus. this new strain combines elements of the previously circulating clade Ib and clade IIb branches, prompting further inquiry into its potential impact on transmission and vaccine effectiveness [[3]].
Health officials in the United Kingdom have identified a new, recombinant strain of mpox in England, highlighting the virus’s potential for ongoing evolution and the importance of continued monitoring. The case involved an individual who recently traveled to Asia, according to the UK Health Security Agency (UKHSA).
Genetic sequencing revealed the virus contains elements from both the clade Ib and clade IIb branches of mpox. While the co-circulation of these clades makes recombination possible, experts say this particular event is noteworthy. “This is a rare event,” explained Professor Geoffrey Smith of the University of Oxford. “For a hybrid virus to be created, the same cell has to be infected simultaneously by both strains, as recombination takes place inside the infected cell.” He added, “This is all the more rare because orthopoxviruses deploy mechanisms to prevent a second infection of a cell already infected by another orthopoxvirus. Therefore, to infect a cell with both viruses, infection with each must occur at a very close time – within hours.”
The UKHSA is currently evaluating the significance of this newly identified strain. Understanding how mpox evolves is crucial for public health preparedness and informing potential vaccine strategies.
In 2022, a global mpox outbreak was largely driven by the clade II strain, which generally causes less severe illness and is often spread through sexual contact. This differed from the historically more virulent clade I strain.
However, toward the end of 2024, an increase in cases linked to the more virulent clade I strain raised concerns, particularly as it appeared to gain the ability to transmit sexually. Both strains share similar symptoms, including fever, muscle aches, headache, and a characteristic rash with blisters or ulcers. However, clade I has demonstrated a higher mortality rate, with up to 10% of infected individuals succumbing to the disease.
A rapid spread of clade I from the Democratic Republic of the Congo (DRC) to neighboring countries prompted the World Health Organization (WHO) to declare mpox a Public Health Emergency of International Concern in August 2024.
The WHO lifted the global emergency designation in September 2025, but recently issued a new alert regarding wider transmission of clade I mpox in several countries where the virus is not typically found, including the United States. This update underscores ongoing public health challenges related to mpox globally. More information about the recent case can be found at UK Health Security Agency, and further analysis is available from Gavi, the Vaccine Alliance.
