The UK government has secured an extra 150,000 doses of the mpox vaccine as a precautionary measure against a new and potentially more dangerous strain of the virus. This new variant, known as Clade 1b, is causing increasing concern due to its spread in Africa and recent isolated cases in Europe and Asia.
Although the UK has not yet reported any cases of the Clade 1b strain, health officials consider the risk to be currently “low.” The World Health Organization (WHO) recently declared the resurgence of mpox a “public health emergency of international concern” due to its spread beyond Africa.
Given the long incubation period of mpox and its potential for global dissemination, the UK is preparing for the possibility of its arrival. In addition to procuring more vaccines, the UK Health Security Agency (UKHSA) has released a risk assessment for Clade 1b, outlining possible scenarios for an outbreak in the UK.
Professor Susan Hopkins, chief medical adviser at the UKHSA, emphasized the importance of vaccination and preparedness. She noted that efforts are underway to ensure that healthcare professionals can promptly identify cases, rapid testing is available, and protocols for safe clinical care and preventing further transmission are in place.
The risk assessment considers the ongoing global outbreak of Clade 2 mpox, which has resulted in over 100,000 cases worldwide and nearly 4,000 in the UK. This strain has predominantly affected gay and bisexual men, and a targeted vaccination campaign starting in 2022 has successfully reduced transmission rates in the UK.
Clade 1b, however, presents new challenges. It has been spreading among heterosexual partners, particularly sex workers, and causing outbreaks within families and among children. Although less than 1% of cases are fatal, there is limited information on whether Clade 1b is more infectious or dangerous compared to Clade 2.
The UKHSA has outlined three potential scenarios for how Clade 1b might impact the UK:
- Less Infectious Scenario: Clade 1b could be less transmissible than Clade 2, resulting in isolated cases and small clusters that can be controlled through contact tracing and isolation.
- Controllable Epidemic Scenario: If Clade 1b is as infectious as Clade 2, it could lead to a “controllable epidemic” with established transmission chains among sexual networks. In this case, targeted vaccination of high-risk individuals and ring vaccination of contacts would help manage the outbreak.
- Highly Infectious Scenario: If Clade 1b is more transmissible than Clade 2, it could lead to widespread outbreaks in close-contact settings such as homes, nurseries, care facilities, and prisons. In this scenario, only a nationwide vaccination campaign would be effective, but current global vaccine supplies are insufficient for such an extensive effort.
The UK continues to monitor the situation closely and prepare for various potential outcomes as it navigates the evolving threat of mpox.
