Guidance

Risk assessment methodology to inform international travel traffic light system

Updated 29 October 2021

The UK Health Security Agency (UKHSA), in partnership with the devolved administrations, has developed a dynamic public health risk assessment methodology to inform ministerial decisions on red list countries and territories, and the associated border measures.

This methodology has been endorsed by the UKHSA technical board (the 4 UK Chief Medical Officers and their relevant specialists, such as Chief Scientific Advisers).

UKHSA reviews over 250 countries, territories, and island groups, with territories and island groups being treated as distinct from their associated mainland where data allows. All collect, analyse, and share data differently – data is not always comparable between them, making analysis and assessment challenging. Therefore, it is important to analyse a range of qualitative and quantitative indicators to assess that country, territory, island group. As a result, UKHSA does not use a mechanical quantitative approach to assessment with hard thresholds. Instead, a framework is used to consider countries in a consistent way, bringing together a range of qualitative and quantitative indicators to provide an overall judgement on risk.

As a precautionary approach, countries, territories, and island groups are assumed to be medium public health risk unless there is specific evidence to suggest they are:

• low public health risk to the UK from all coronavirus (COVID-19) strains – that is, low assessed prevalence, good surveillance and no evidence of community transmission of variants that pose a significant public health risk to the UK (see, for example, UKHSA’s risk assessment framework for more information)
• high public health risk to the UK from known variants of concern (VOCs), known emerging or high-risk variants under investigation (VUIs) or because of very high (or rapidly increasing) and unexplained prevalence of COVID-19

The methodology consists of 4 parts:

• variant assessment
• triage
• risk assessment
• outcomes that inform ministerial decisions

Variant assessment

UKHSA undertakes regular monitoring and evaluation of new variants. There are many variants of SARS-CoV-2 (the virus that causes COVID-19), most of which are not of additional concern.

If a variant is identified that is considered to have concerning properties, it is raised for formal investigation. At this point it is designated by UKHSA as a Variant Under Investigation (VUI).

Following a risk assessment with the relevant expert committee, the variant may be designated as a Variant of Concern (VOC).

This assessment considers several factors including:

• transmissibility
• severity of disease
• escape from natural immunity
• escape from vaccine-induced immunity
• effect on therapeutics
• zoonotic emergence (jumped from animal to human)
• current epidemiology

Further information on the variants of concern and variants of interest being tracked by UKHSA can be found here.

UKHSA also publishes risk assessments of variants on regular basis.

Triage

Selects a list of countries and territories for further risk assessment (‘deep dives’). This stage considers a range of indicators, including:

• testing rates per 100,000 population
• weekly case rates per 100,000 population
• test positivity
• evidence of variants in country and territory
• exported cases of variants to the UK and elsewhere
• genomic sequencing capability
• strong travel links with countries and territories known to have community transmission of a variant

With the exception of Island Groups and some British Overseas Territories (BOTs), all countries and territories are passed through triage.

Further risk assessment

All countries and territories that pass triage undergo a more comprehensive risk assessment alongside the Island Groups and some BOTs using additional quantitative and qualitative information (for example, from publicly available platforms such as GISAID and the World Health Organization (WHO), host government websites, UK mandatory testing data and travel data) taking into account data availability (including timeliness and transparency), limitations and biases (for example, how representative the data is and its granularity).

This information comes from a range of sources, many of which are publicly available, including:

• GISAID (for variants detected) – the data used to inform the risk assessments is available to registered GISAID users that log in via the web portal and uses data based on specimen date (rather than upload date) and lineage
• WHO (for case rates)
• Our World in Data dashboard (for vaccination rates)
• Weekly statistics for NHS Test and Trace (Table 21 of the accompanying data tables, for details of the number arrivals testing positive and variants detected amongst arrivals)
• host government websites (varies by country but may include testing rates, details around variants detected in-country and testing/sequencing strategies)

The vast majority of data used to inform the risk assessment is in the public domain. However, some data cannot be published due to the privacy risks that disclosure may have on individuals or groups. Similarly, privately shared data from other governments or organisations cannot be published due to the undertakings given when obtaining the data.

Outcome

To support decision making, UKHSA focuses the final assessment around 3 main criteria so that ministers know where the risks lie:

• genomic surveillance capability
• COVID-19 transmission risk
• variant transmission risk

Travel connections with the UK and details of the in-country and territory vaccination profile are included as contextual information.

The quality, quantity and transparency of reported data is considered as part of the assessment to provide a statement of confidence. The overall public health risk assessment and confidence statement are both presented on a 5-point scale (very low, low, medium, high and very high).

Decisions on red list assignment and associated borders measures are taken by ministers. Ministers will take the UKHSA risk assessments into account alongside wider public health factors to inform watchlists and make their decisions.

A summary of the data used to inform specific country decisions can be found here.

This methodology will evolve to reflect the changing pattern of the COVID-19 epidemic and as the UKHSA incorporates new scientific insights, new data sources, and new analyses that become available.

The methodology is subject to quarterly review (as a minimum) by the UKHSA technical board. The last review was in September 2021.