HCID status of mpox (monkeypox)monkeypox

Information on the status of mpoxmonkeypox 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.

ReviewsReview in relation to mpoxmonkeypox

In June 2022

The2022, 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 ACDPcommittee recommendednoted that allfuture importations of Clademonkeypox IIfrom MPXV (formerly West AfricanAfrica clade) should nostill longer be classified as an an HCID.

ACDP recommendedas the clinical outcomes might not necessarily be benign, and that monkeypox caused by Clade I (formerly known as Central African or Congo basin clade) should remain an an HCID. The 4 nations public health agencies havediscussed reviewed this advice and agreed with the view of of ACDP.

There is a lack of clinical outcome data for cases of monkeypox caused by strains outside of the current outbreak. Evidence suggests that the strain of monkeypox responsible for the current outbreak is associated with lower mortality and less serious illness than previously observed with monkeypox. Therefore, in September 2022, UKHSA updated the definition of HCID to encompass all cases outside of the current outbreak strain as described below.

Different types of MPXVmonkeypox

MPXVThere isare currentlydifferent strains of monkeypox across the world. These are genetically divided into 23 main genetic groups (Clades II, IIa and II),IIb), which subdivide into multiple lineages.

WHO clade classification (lineage)HCID*?
Clade I (all)Yes
Clade IIa (all)Yes
Clade IIb (B.1 lineage)No
Clade IIb (non-B.1 lineages)Yes

*High consequence infectious disease in the UK. See Genomic epidemiology of monkeypox virus for further information.

Clade I

Originally known as the ‘Central African’ or ‘Congo Basin’ clade, this is more likely to cause severe mpoxmonkeypox disease. ToNo date, there have been no Clade I cases infrom the UK, and this clade hashave not been implicatedseen in thenon-endemic outbreakcountries thatduring startedthe in2022 mid-2022.outbreak.

Clade II

This was formerly known as the ‘West African’ cladeclade. andAppears 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 2022 global outbreakoutbreak. that started in mid 2022. There are several lineages of Clade IIb that are genetically distinct.distinct:

  • Clade TheIIb, B.1 lineagelineage: this is the main outbreak strain currently in circulation in the UK – all UK-acquired mpox(that is, non-travel associated) monkeypox cases genetically sequenced so far are part of this lineage.


  • Clade smallIIb, numberall oflineages Cladethat IIb,are non-B.1not lineageB.1: a small number of travel-associated cases have also been identified.

    Furthercaused informationby onnon-B.1 thelineages genomic epidemiologythe severity of MPXVdisease iscaused available.

    by this lineage, and its transmission characteristics, are not currently fully understood

Operational definitions

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

  • confirmed Clade I MPXV, or
  • not known and:
    • there is a travel history to West or Central Africa, or a link to a traveller from those regions and/or
    • there is ana epidemiological link to a case ofwhich Cladeis Iknown mpoxto be outside the current outbreak strain (Clade IIb, B.1 lineage) and/or
    • the case results from a new zoonotic jump in any country or setting
  • known, and is outside the current outbreak strain (Clade IIb, B.1 lineage)

MpoxMonkeypox 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 West or Central Africa
    • there is no link to a traveller from West or Central Africa
    • the case has not resulted from a new zoonotic jump


  • known, assessingand ais patient for possible mpox, ensure you assess the travelcurrent andoutbreak contactstrain history(Clade asIIb, aboveB.1 (see also the case definitions).

  • All cases meeting the operational definition of an an HCID should should be managed as an HCID. They should all be discussed with the Imported Fever Service (0844 778 8990).

    When Casesassessing where the lineage is unknown, but who have a travelpatient orfor contactpossible historymonkeypox, asensure above,you shouldfollow be discussed with the Importedrelevant Feveradvice Serviceon astaking soonthe aspatient’s possiblehistory toin ensurethe appropriatecase testing and escalation.definitions.

    Other implications

    HCID network

    MostThe 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 of HCID units units in the assessment and management of cases requiring admission to hospital. This reflects the potential for severe disease duebeing tocaused anyby the current outbreak clade in vulnerable groups.groups Inand addition,the thereneed mayto beappropriately specificmanage infectionadmissions controlto riskshospital, inrecognising the risk to staff and other vulnerable patients.

    Most patients with extensivemild diseasesymptoms wherewho inputare fromable theto HCIDself-isolate, networkwill may be helpful.

    Waste,managed transporton andan laboratoryoutpatient requirements

    basis with appropriate oversight via virtual ward or similar such arrangements.

    There is no change to waste, transport or laboratory regulatory requirements as a result of the the HCID derogation. Byderogation; internationalhowever, agreement,the Department for Transport has recently amended transport and packaging classifications so that samples and waste from allmonkeypox mpox cases are now classified as Category B for(as transportper andclinical wastewaste). management. Laboratory cultures of MPXVmonkeypox 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 2320 JanuarySeptember 20232022 + 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.