HCID status of monkeypox

Information on the status of monkeypox 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.

Review in relation to monkeypox

In June 2022, the Advisory Committee on Dangerous Pathogens (ACDP) recommended that the strain of monkeypox currently in community transmission within the UK should no longer be classified as an HCID.

The committee noted that future importations of monkeypox from West Africa should still be classified as an HCID as 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 HCID. The 4 nations public health agencies discussed this advice and agreed with the view 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 monkeypox

There are different strains of monkeypox across the world. These are genetically divided into 3 main groups (Clades I, IIa and 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 monkeypox disease. No cases from this clade have been seen in non-endemic countries during the 2022 outbreak.

Clade II

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

Clade IIa

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 outbreak. There are several lineages of Clade IIb that are genetically distinct:

  • Clade IIb, B.1 lineage: this is the main outbreak strain currently in circulation in the UK – all UK-acquired (that is, non-travel associated) monkeypox cases genetically sequenced so far are part of this lineage
  • Clade IIb, all lineages that are not B.1: a small number of travel-associated cases have been caused by non-B.1 lineages – the severity of disease caused by this lineage, and its transmission characteristics, are not currently fully understood

Operational definitions

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

  • 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 a link to a case which is known to 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)

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

  • 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, and is the current outbreak strain (Clade IIb, B.1 lineage)

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

When assessing a patient for possible monkeypox, ensure you follow the relevant advice on taking the patient’s history in the case definitions.

Other implications

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 being caused by the current outbreak clade in vulnerable groups and the need to appropriately manage admissions to hospital, recognising the risk to staff and other vulnerable patients.

Most patients with mild symptoms who are able to self-isolate, will be managed on an outpatient 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 HCID derogation; however, the Department for Transport has recently amended transport and packaging classifications so that samples and waste from monkeypox cases are now classified as Category B (as per clinical waste). Laboratory cultures of monkeypox remain classified as Category A.

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 20 September 2022 + show all updates
  1. Updated information about the definition of HCID.

  2. First published.