HCID status of mpox (monkeypox)

Information on the status of mpox as a high consequence infectious disease (HCID).


A high consequence infectious disease (HCID) is defined as:

  • an acute infectious disease
  • typically having a high case-fatality rate
  • not always having effective prophylaxis or treatment
  • often difficult to recognise and detect rapidly
  • able to spread in the community and within healthcare settings
  • requiring an enhanced individual, population and system response to ensure it is managed effectively, efficiently and safely

HCID status is conferred by the UK 4 nations public health agencies, with advisory committee input as required. It is used to determine the appropriate clinical and public health response pathways. It has no standing in law. It does not of itself affect the classification of the pathogen in terms of hazard group, the management of waste or transport requirement.

Reviews in relation to mpox

June 2022

The Advisory Committee on Dangerous Pathogens (ACDP) recommended that the strain of monkeypox virus (MPXV) currently in community transmission within the UK (Clade IIb, B.1 lineage) should no longer be classified as an HCID.

January 2023

The ACDP recommended that all of Clade II MPXV (formerly West African clade) should no longer be classified as an HCID.

ACDP recommended that Clade I (formerly known as Central African or Congo basin clade) should remain an HCID. The 4 nations public health agencies have reviewed this advice and agreed with the view of ACDP.

Different types of MPXV

MPXV is currently divided into 2 main genetic groups (Clades I and II), which subdivide into multiple lineages.

Clade I

Originally known as the ‘Central African’ or ‘Congo Basin’ clade, this is more likely to cause severe mpox disease. To date, there have been no Clade I cases in the UK, and this clade has not been implicated in the outbreak that started in mid-2022.

Clade II

This was formerly known as the ‘West African’ clade and appears to cause less severe mpox disease in humans than Clade I. Clade II has been further subdivided into Clades IIa and IIb.

Clade IIa

Isolates from this clade have previously been reported in West Africa. No cases from this clade have been seen in the 2022 outbreak.

Clade IIb

Clade IIb is the group of variants largely circulating in the global outbreak that started in mid 2022. There are several lineages of Clade IIb that are genetically distinct. The B.1 lineage is the main outbreak strain currently in circulation in the UK – all UK-acquired mpox cases genetically sequenced so far are part of this lineage.

A small number of Clade IIb, non-B.1 lineage travel-associated cases have also been identified.

Further information on the genomic epidemiology of MPXV is available.

Operational definitions

Confirmed or highly probable cases of mpox are considered an HCID if the lineage responsible is:

  • confirmed Clade I MPXV, or
  • not known and:
    • there is a travel history to Central Africa, or a link to a traveller from those regions and/or
    • there is an epidemiological link to a case of Clade I mpox and/or
    • the case results from a new zoonotic jump in any country or setting

Mpox is not considered an HCID where the lineage responsible is:

  • confirmed as Clade II MPXV, or
  • not known, and all the following conditions apply:
    • there is no history of travel to Central Africa
    • there is no link to a traveller from Central Africa
    • the case has not resulted from a new zoonotic jump

When assessing a patient for possible mpox, ensure you assess the travel and contact history as above (see also the case definitions).

All cases meeting the operational definition of an HCID should be discussed with the Imported Fever Service (0844 778 8990). Cases where the lineage is unknown, but who have a travel or contact history as above, should be discussed with the Imported Fever Service as soon as possible to ensure appropriate testing and escalation.

Other implications

HCID network

Most patients with non-HCID mpox who have mild symptoms and who are able to self-isolate will be managed as outpatients with follow-up via a virtual ward or similar, by local sexual health or infection services. However, the NHS in all 4 nations will continue to draw on the expertise of HCID units in the assessment and management of cases requiring admission to hospital. This reflects the potential for severe disease due to any clade in vulnerable groups. In addition, there may be specific infection control risks in patients with extensive disease where input from the HCID network may be helpful.

Waste, transport and laboratory requirements

There is no change to waste, transport or laboratory regulatory requirements as a result of the HCID derogation. By international agreement, samples and waste from all mpox cases are classified as Category B for transport and waste management. Laboratory cultures of MPXV remain classified as Category A.

Personal protective equipment (PPE)

There is no automatic change to personal protective equipment (PPE). Recommendations are outlined in the 4 nations principles document and relevant national infection prevention and control (IPC) guidance.

There is no automatic change to the public health response. The decisions on stringency of approach remain with the incident management team (IMT) and will be decided on the basis of the public health risk assessment.

Published 5 July 2022
Last updated 23 January 2023 + show all updates
  1. Updated in line with the HCID derogation of all Clade II mpox.

  2. Updated information about the definition of HCID.

  3. First published.