Derogation of clade I mpox
Source: gov.uk (2025-03-19)

Urgent public health message advising that clade I mpox no longer meets the criteria of a high consequence infectious disease (HCID).

The Advisory Committee on Dangerous Pathogens (ACDP) recently assessed evidence gathered by UKHSA for clade I mpox and advised that it no longer met the criteria of a high consequence infectious disease (HCID). Therefore, the Chief Medical Officers (CMOs) of the 4 nations have agreed that mpox will no longer be managed as an HCID within healthcare settings.

Mpox remains a serious infection for some individuals and remains a World Health Organization (WHO) public health emergency of international concern (PHEIC). The UK’s strategic goal continues to be to eliminate person-to-person transmission of mpox in the UK. Therefore, there will be ongoing public health management of cases and contacts, including vaccination where appropriate.

Actions for the NHS

1. Providers should be aware that all mpox (clade I and clade II) is no longer classed as an HCID.

2. Providers should ensure that relevant clinical services – including primary care, urgent care, sexual health services, paediatrics, obstetrics, and emergency departments (EDs) - are aware of the information in this public health message, and that a differential diagnosis of mpox infection (caused by the virus MPXV) is considered wherever appropriate.

3. Providers should ensure that they have adequate stocks of appropriate personal protective equipment (PPE) for use during the assessment and treatment of patients presenting with suspected mpox, and for use by cleaners of rooms or areas where suspected or confirmed cases have been. Staff must be trained on the safe removal of PPE to avoid self-contamination.

4. Providers should ensure there is a clinical pathway for appropriate isolation and management of suspected mpox cases within their setting, incorporating the information provided in this alert and their relevant country’s national infection prevention manual. This should include:
- isolation of the patient
- liaison with local infection prevention and control (IPC) teams
- arrangements for discussion of the case with local infectious disease, microbiology or virology consultants
- thorough cleaning and decontamination of rooms or areas where the suspected case has been
5. Registered medical practitioners are reminded that mpox is an urgent notifiable disease. They should ensure that suspected mpox cases are notified to their local health protection team so that appropriate public health measures, including contact identification and management can be considered.

Find out about notification in each nation:
- England (https://www.gov.uk/guidance/notifiable-diseases-and-how-to-report-them#list-diseases)
- Northern Ireland (https://www.niinfectioncontrolmanual.net/notifiable-diseases/)
- Scotland (https://publichealthscotland.scot/population-health/health-protection/notifiable-diseases-health-risk-states-and-infections/overview/)
- Wales (https://publichealthwales.nhs.wales/services-and-teams/aware-health-protection-team/)
6. Integrated Care Boards (ICBs) and commissioners (where this is relevant in the UK) should ensure there are effective pathways in place for post-exposure prophylaxis for high-risk contacts of cases, and ring vaccination where necessary.

7. Providers should ensure there are effective vaccination pathways in place to deliver pre-exposure prophylaxis to staff identified in higher risk occupational groups as set out in the Mpox outbreak: vaccination strategy (https://www.gov.uk/guidance/monkeypox-outbreak-vaccination-strategy).

8. Samples from individuals testing positive for MPXV must be sent for clade differentiation as part of ongoing surveillance and management of risk to the UK from mpox. In England, this is available from the UKHSA Rare and Imported Pathogens Laboratory (RIPL). In the devolved administrations, clade testing is available at the National Laboratories. If clade testing is available locally, laboratories should ensure that the assays are up to date and able to differentiate clades Ia, Ib and II, and that reporting pathways are updated so that clade information is captured through the Second Generation Surveillance System (SGSS).

Background

Mpox is a viral illness caused by MPXV. Cases present with a rash illness which may be mild and localised, or severe and disseminated. The symptoms of mpox begin 5 to 21 days (average 6 to 16 days) after exposure, with initial clinical presentation of fever, malaise, lymphadenopathy and headache. Within 1 to 5 days after the appearance of fever, a rash develops, often beginning on the face or genital area which may then spread to other parts of the body. The rash changes and goes through different stages before finally forming scabs which later fall off. Treatment for mpox is mainly supportive.

Since May 2022, cases of human mpox have been reported in multiple countries that have not previously had MPXV in animal or human populations, including the UK. There are 2 distinct clades of MPXV, clade I and clade II. There have been at least 3 emergences from animal reservoirs leading to sustained human-to-human transmission:
- Global outbreak of clade IIb in gay, bisexual or other men who have sex with men (GBMSM) in 2022 to 2023.
- Regional outbreak of clade Ib in affected African countries, with some exported cases from 2024.
- Outbreak of clade Ia in the Democratic Republic of Congo in 2024.
All MPXV disease was classified as an HCID in 2018, meaning that all suspected and confirmed cases were managed via HCID pathways. In January 2023, ACDP advised that clade II mpox no longer met the criteria for an HCID due to accumulating evidence of low case fatality rate, and mild to moderate severity illness. A further review of evidence in 2025 suggested that the case fatality rate and severity for clade Ib mpox is similar to clade IIb mpox, and in February 2025 ACDP recommended that clade I mpox should also no longer be classified as an HCID.

The CMOs of the 4 nations have agreed that mpox will no longer be managed as an HCID within healthcare settings. This means that all mpox (clade I and clade II) is no longer classed as an HCID.

Clinical assessment

Additional details on mpox clinical features can be found at Mpox: background information (https://www.gov.uk/guidance/monkeypox#clinical-features).

Consider mpox where a case presents with:

1. a prodrome (fever, chills, headache, exhaustion, myalgia, arthralgia, backache, lymphadenopathy) in an individual with contact with a confirmed or suspected case of mpox in the 21 days before symptom onset

Or:

2. an mpox-compatible rash anywhere on the skin (face, limbs, extremities, torso) or mucosae (including oral, genital, anal), or symptoms of proctitis, and at least one of the following in the 21 days before symptom onset:
- recent new sexual partner
- contact with known or suspected case of mpox
- a travel history to a country where mpox is currently common (https://www.gov.uk/guidance/clade-i-mpox-affected-countries) - this does not include people transiting through the affected country where they do not leave the airport
- link to an infected animal or meat
Or:

3. an mpox-compatible rash anywhere on the skin (face, limbs, extremities, torso) or mucosae (including oral, genital, anal), or symptoms of proctitis, where there is no risk factor and no alternative common differential diagnosis [note 1]. These patients should be discussed with local infection services to determine the approach to investigation and management.

Note 1: alternative common differential infections include varicella zoster virus (which causes chickenpox or shingles), herpes simplex virus, and enterovirus (which causes hand, foot and mouth disease), and bacteria such as staphylococcal and streptococcal infections.

UKHSA’s mpox resource collection (https://www.gov.uk/government/collections/monkeypox-guidance) will be kept up to date to assist NHS clinicians in diagnosis.

Management of possible cases

Clinicians should be alert to the possibility of MPXV infection in patients presenting with compatible symptoms. Clinicians treating patients with suspected mpox may discuss the case with local infection specialists.

Infection specialists may wish to discuss possible mpox cases with the UKHSA Imported Fever Service (IFS) on xx-xxxx-xxxx for clinical advice, for example in a patient who is severely immunocompromised, paediatric, pregnant or from a high risk setting such as shared accommodation.

Provider risk assessments

Risk assessments must be conducted in all areas where there is possibility of encountering or caring for individuals with clinically suspected or confirmed cases of mpox.

These assessments should be carried out by a competent person who has the necessary skills, knowledge, and experience to identify and manage the risks associated with mpox. This individual could be the employer, or someone specifically appointed for this task.

The results of these risk assessments should be communicated to all employees who may be involved in the care and management of mpox cases. This information can also be integrated into local risk management systems.

PPE requirements

PPE requirements are set out in the National infection prevention and control manual (NIPCM) for England (https://www.england.nhs.uk/national-infection-prevention-and-control-manual-nipcm-for-england/) for non HCID mpox and in the following documents for devolved administrations:

Scotland (https://www.nipcm.scot.nhs.uk/)

Wales (https://phw.nhs.wales/services-and-teams/antibiotics-and-infections/nipcm/)

Northern Ireland (https://www.niinfectioncontrolmanual.net/)

PPE is also required for those cleaning areas or rooms where a suspected or confirmed mpox case has been.

Supplementary information on IPC

The requirements for suitable and adequate PPE in the ambulance service may differ due to the settings and conditions in which they operate.

For suspected or confirmed cases attending ambulatory healthcare services (for example outpatients, EDs, urgent care centres, general practice, sexual health clinics), patients should be placed in a single room for assessment. The case should be provided with a fluid-resistant surgical mask (FRSM) to wear if possible, for example if they are clinically stable and able to tolerate a mask.

Ongoing public health management

Mpox remains a WHO PHEIC.

The UK’s strategic goal is to eliminate person-to-person transmission of MPXV in the UK, and an updated MPXV control and elimination strategy is in preparation.

UKHSA and the devolved nations’ public health agencies will continue to monitor emerging evidence, conduct surveillance, adapt guidance as needed, encourage vaccine uptake in those eligible, and advise on the public health management of cases and their contacts to minimise onward transmission.

Approvals

This urgent public health message has been approved by:
- Professor Susan Hopkins, Chief Medical Advisor, UKHSA
- Professor Stephen Powis, National Medical Director, NHS England
- Professor Thomas Waite, DCMO, England
- Professor Nicola Steedman, DCMO, Scotland
- Professor Lourda Geoghegan, DCMO, Northern Ireland
- Dr Keith Reid, DCMO, Wales