Michael Coston
Editor, Senior Moderator
UKHSA: Updated Risk Assessment On Mpox Clade Ib
Credit UK HSA
#18,926
Over the past 10 days we've seen signs of community transmission of the emerging Mpox Clade Ib virus reported both in the United States (see Los Angeles County Reported 3 (locally acquired) Clade I Mpox Cases) and in Europe (see ECDC Statement & Threat Assessment Brief Following Recent Reports of Local Transmission of Mpox Clade Ib in Europe).
While local (usually household) transmission outside of Africa has been previouslyl reported by a few countries, it has been rare, and has nearly always been traced to known contact with a recent traveler from Africa.
In response to these recent reports of community transmission, yesterday the UK's Health Security Agency (UKHSA) published an updated risk assessment, their first since December of 2024.
While this 20-page document provides a number of plausible scenarios, it starts off with the following.
Summary
Since the last technical assessment on 19 December 2024:
• the epidemiology of clade I mpox may have changed with person-to-person transmission now occurring outside the African Region including amongst specific gay, bisexual and other men-who-have-sex-with-men (GBMSM) networks in at least 2 other WHO regions (EURO and PAHO)
• the probability of importation into the UK has increased from medium to high
• the risk of onwards transmission in the UK is likely to be controlled to some degree by the existing GBMSM vaccination programme and remains low to medium at present; however there are significant uncertainties in this assessment relating to the circulating virus properties, the groups at risk and the level and duration of immunity from natural infection or vaccine.
A year ago the UK released their Updated Mpox Technical Briefing #9 which presented 3 possible scenarios for the spread of Mpox in the UK ranging from the least to most impactful.
A) incursions and small clusters of cases,
B) a controllable epidemic, and
C) community transmission
At that time, the UKHSA stated that `. . . Currently indicators are most compatible with scenario A . . .'.
But less than 4 months later (Dec 2024), this had shifted to " . . . The indicators are currently most compatible with scenario B – a virus with moderate transmissibility (similar to or slightly exceeding the transmissibility of the clade II outbreak).'
Today's update, while acknowledging the possibility of seeing a wider epidemic (Scenario C), keeps the previous assessment, stating:
Since the last technical briefing published on 19 December 2024, indicators continue to be assessed as being most compatible with Scenario B based on the transmissibility of the virus.
While our assessment is that globally we are in Scenario B (a controlled epidemic), in Africa initial transmission is among adults driven by close contact, including sexual contact, with a shift to younger age groups where initial clusters are not controlled. It is uncertain whether community transmission is self-sustaining without sexual transmission seeding outbreaks.
You'll want to follow the link to read the full report, which discusses uncertainties regarding both transmission of the virus and the effectiveness and duration of protection from the current JYNNEOS vaccine.
(For more background see Preprint: The Two-dose MVA-BN Mpox Vaccine Induces a Nondurable and Low Avidity MPXV-specific Antibody Response).
The report concludes with the following:
4.2 Future assessment
It is highly likely that the number of imported cases outside of Africa will increase in the next 6 months (moderate confidence). There has been a deterioration in the epidemiology of the outbreak in Africa in the last 12 months. The number of countries with community transmission of clade I mpox has increased from 1 to 9 countries, some of which have greater connectivity to Europe (For example, Uganda and Kenya).
It is likely there will be an increase in secondary transmission and larger outbreaks are likely to occur in at risk populations outside of Africa in the next 6 months (low confidence).
There are signals that there may be increasing transmission outside of Africa, including possible undetected transmission in countries. Additionally, there is evidence of community transmission of clade I mpox within the GBMSM community.
https://afludiary.blogspot.com/2025/10/ukhsa-updated-risk-assessment-on-mpox.html
Credit UK HSA
#18,926
Over the past 10 days we've seen signs of community transmission of the emerging Mpox Clade Ib virus reported both in the United States (see Los Angeles County Reported 3 (locally acquired) Clade I Mpox Cases) and in Europe (see ECDC Statement & Threat Assessment Brief Following Recent Reports of Local Transmission of Mpox Clade Ib in Europe).
While local (usually household) transmission outside of Africa has been previouslyl reported by a few countries, it has been rare, and has nearly always been traced to known contact with a recent traveler from Africa.
In response to these recent reports of community transmission, yesterday the UK's Health Security Agency (UKHSA) published an updated risk assessment, their first since December of 2024.
While this 20-page document provides a number of plausible scenarios, it starts off with the following.
Summary
Since the last technical assessment on 19 December 2024:
• the epidemiology of clade I mpox may have changed with person-to-person transmission now occurring outside the African Region including amongst specific gay, bisexual and other men-who-have-sex-with-men (GBMSM) networks in at least 2 other WHO regions (EURO and PAHO)
• the probability of importation into the UK has increased from medium to high
• the risk of onwards transmission in the UK is likely to be controlled to some degree by the existing GBMSM vaccination programme and remains low to medium at present; however there are significant uncertainties in this assessment relating to the circulating virus properties, the groups at risk and the level and duration of immunity from natural infection or vaccine.
A year ago the UK released their Updated Mpox Technical Briefing #9 which presented 3 possible scenarios for the spread of Mpox in the UK ranging from the least to most impactful.
A) incursions and small clusters of cases,
B) a controllable epidemic, and
C) community transmission
At that time, the UKHSA stated that `. . . Currently indicators are most compatible with scenario A . . .'.
But less than 4 months later (Dec 2024), this had shifted to " . . . The indicators are currently most compatible with scenario B – a virus with moderate transmissibility (similar to or slightly exceeding the transmissibility of the clade II outbreak).'
Today's update, while acknowledging the possibility of seeing a wider epidemic (Scenario C), keeps the previous assessment, stating:
Since the last technical briefing published on 19 December 2024, indicators continue to be assessed as being most compatible with Scenario B based on the transmissibility of the virus.
While our assessment is that globally we are in Scenario B (a controlled epidemic), in Africa initial transmission is among adults driven by close contact, including sexual contact, with a shift to younger age groups where initial clusters are not controlled. It is uncertain whether community transmission is self-sustaining without sexual transmission seeding outbreaks.
You'll want to follow the link to read the full report, which discusses uncertainties regarding both transmission of the virus and the effectiveness and duration of protection from the current JYNNEOS vaccine.
(For more background see Preprint: The Two-dose MVA-BN Mpox Vaccine Induces a Nondurable and Low Avidity MPXV-specific Antibody Response).
The report concludes with the following:
4.2 Future assessment
It is highly likely that the number of imported cases outside of Africa will increase in the next 6 months (moderate confidence). There has been a deterioration in the epidemiology of the outbreak in Africa in the last 12 months. The number of countries with community transmission of clade I mpox has increased from 1 to 9 countries, some of which have greater connectivity to Europe (For example, Uganda and Kenya).
It is likely there will be an increase in secondary transmission and larger outbreaks are likely to occur in at risk populations outside of Africa in the next 6 months (low confidence).
There are signals that there may be increasing transmission outside of Africa, including possible undetected transmission in countries. Additionally, there is evidence of community transmission of clade I mpox within the GBMSM community.
https://afludiary.blogspot.com/2025/10/ukhsa-updated-risk-assessment-on-mpox.html