Outbreak of an emerging infectious disease

Impact 5
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risk indicator
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Impact & Likelihood
Impact key
5 Catastrophic
4 Significant
3 Moderate
2 Limited
1 Minor
Likelihood key
5 >25%
4 5-25%
3 1-5%
2 0.2-1%
1 <0.2%


Emerging infectious diseases include new or newly recognised diseases and could result in large numbers of people falling ill. Some recently emerged diseases, such as Ebola and Middle East Respiratory Syndrome, are classified as High Consequence Infectious Diseases. These are acute infectious diseases that typically have a high case fatality rate and may or may not have effective prophylaxis or treatment and can be difficult to recognise or diagnose rapidly. They require an enhanced individual, population and system response to ensure management is effective, efficient and safe. The UK Health Security Agency and NHS responders have well-tested response capabilities to detect, contain and treat novel infectious diseases.


The reasonable worst-case scenario is based on a novel respiratory- transmitted virus that emerges zoonotically (from animals to humans) in another country and causes a regional epidemic. This covers diverse virus families, which may acquire some degree of human-to-human transmission, such as influenza viruses, coronaviruses and nipah viruses. However, we must be prepared for a disease spread via any of the 5 main routes of transmission: respiratory, blood (including sexual contact), close contact oral (food and water) and by vectors such as mosquitos.

There would be a small number of cases imported into the UK before border measures are applied, which could result in an outbreak of up to 2,000 cases with a case fatality rate of up to 25%. A significant number of contacts, up to 200,000, would need to be traced, isolated or monitored depending on exposure. Non-pharmaceutical interventions, rapid isolation and contact tracing activities would need to follow on from the initial border measures, with limited virus transmissibility bringing the outbreak under control.

Failure to contain the outbreak would result in a large epidemic in the UK, or a pandemic.

Key assumptions

It is assumed that the novel pathogen causing the epidemic would emerge abroad, with no effective treatment or vaccine.
It is assumed that the pathogen would be previously unknown or not normally found within the UK, resulting in a significant outbreak. Infections would be transmitted by the respiratory route, there would be limited human-to-human transmissibility and the outbreak is contained regionally. The outbreak would last between 2 to 6 months. Infected individuals would show identifiable and visible symptoms at the same time as, or preceding, the risk of transmission.


There are a range of different transmission routes and disease severities, which are reflected in the variations of a viral haemorrhagic fever, vector-borne disease and zoonotic infection.

Response capability requirements

The capability response would be focused on containment (stopping further transmission and reducing cases to zero).
This would include the quick implementation of appropriate border measures, with a focus on scalable isolation capabilities, disease surveillance and early detection. There would be a need for personal protective equipment supplies, scalable diagnostics (both lab and rapid testing) and decontamination services in place
to prevent cases from rising. A national communications plan would also be needed to increase awareness and encourage good hygiene. Our response capability would need to be able to channel significant research and development resource to developing tests, vaccines and therapeutics.


Long-term impacts would not be understood until several months or up to years later, with possible long-term consequences on the health and social care system.