UK Covid Alert levels explained

One of the key objectives of the UK Health Security Agency (UKHSA) is to provide advice to the UK chief medical officers (CMOs) who in turn advise ministers on the UK COVID-19 alert level.

The alert levels are:

• level 1: COVID-19 is not known to be present in the UK
• level 2: COVID-19 is present in UK, but the number of cases and transmission is low
• level 3: a COVID-19 epidemic is in general circulation
• level 4: a COVID-19 epidemic is in general circulation; transmission is high and direct COVID-19 pressure on healthcare services is widespread and substantial or rising
• level 5: as level 4 and there is a material risk of healthcare services being directly overwhelmed by COVID-19

This document outlines the criteria used by UKHSA as it considers its recommendation for the CMOs. The initial methodology was developed following consultation with national public health experts, reviewed and informed by the Scientific Advisory Group for Emergencies (SAGE) and agreed by the UK’s CMOs.

The methodology will evolve as UKHSA learns from current operations and as information streams develop. It is therefore subject to future review by the UKHSATechnical Board, chaired on a rotating basis by the 4 UK CMOs.

Approach

UKHSA’s approach is focused on the criteria to move between levels, rather than criteria that define an individual level. Also considered are thematic risk assessments which assess risk held in areas which may not be captured by indicators alone. The indicators and risk assessments presented below are considered in the context of a range of measures. Determining the alert level is not an automated or purely statistical process. The approach aims to blend expert judgement and risk assessment with the more quantifiable indicators and thresholds outlined below. This informs an overall assessment of the situation and an alert level recommendation to CMOs.

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The UK COVID-19 alert level is focussed on data that directly relates to COVID-19 impacts. The one exception is the move between Level 4 and Level 5, where the UKHSAand CMOs consider all source pressures as this informs the probability of healthcare services being overwhelmed.

Our operational aim is to avoid unnecessary, unpredictable or frequent changes to the alert level, account for the nationwide complexity of the epidemic and reflect our evolving understanding of COVID-19 and its transmission.

Timing

It will sometimes be necessary to escalate the alert level as rapidly as possible, to signal an urgent, escalating national public health crisis. Conversely, as the risk posed by COVID-19 drops, it will be important to ensure changes to the alert level are undertaken in a stable fashion and that a long-term downward trend in new infections has been established. As a guiding principle, UKHSA will ensure that most, if not all, indicators have been met and that thematic risk assessments are not high risk when recommending to CMOs a reduction in the alert level.

Following any recommendation to de-escalate, a minimum of 4 weeks is allowed before any subsequent recommendation to de-escalate further. During the 4 weeks immediately following a de-escalation, epidemic trajectory and risk assessments will continue to be monitored and a recommendation to escalate may still be made during this time if required.

Indicators for escalation and de-escalation of UK COVID-19 alert levels

A range of indicators and thresholds are used to support the underpinning analysis for alert level recommendations. Though a recommendation to raise the alert level could, in extremis, be made based a single indicator alone, it is most likely to be made based on a combination of the indicators described for each threshold along with risk assessments.

Escalation and de-escalation indicators and thresholds for each alert level are listed below.

Alert Level 1

There is a single holding indicator, with recommendation for level 1 only possible if that indicator is met:

• is there reliable evidence and consensus between UK CMOs and UKHSA that COVID-19 is no longer present in the UK?

Rationale

A recommendation to de-escalate to alert level 1 would require consensus between UK CMOs and UKHSA that COVID-19 is no longer present in the UK. Evidence will be considered using information provided by health protection and central surveillance teams in each UK nation and other sources as appropriate. Should the above indicator not be met, the alert level recommendation would be escalate to, or remain at, level 2.

Escalating from level 2 to level 3

Indicators

Is the:

• UK weekly case rate more than 50 per 100,000 population?
• national R reliably estimated to be ≥1?
• doubling time of confirmed new infections less than 7 days?

Rationale

At this level many statistical or mathematical measures, such as R, are unlikely to be reliable. A short doubling time of confirmed new infections would suggest the contact tracing and isolation programme is not sufficiently containing outbreaks. A weekly case rate is also considered. At these lower alert levels the regional thematic risk assessment will be of particular significance and may consider evidence from public health surveillance systems and outbreak numbers

Sources include laboratory test results, public health surveillance systems and modelling from SPI-M/SAGE.

Escalating from level 3 to level 4

Indicators:

• is the UK weekly case rate more than 250 per 100,000 population?
• is the national R reliably estimated to be R>1?
• is the doubling time of confirmed new infections less than 7 days?
• are there more than 30,000 estimated new infections in the UK per day?
• are COVID-19 related hospital admissions increasing at ≥25% over the same 7-day period?
• is COVID-19 related hospital occupancy increasing at ≥25% over the same 7-day period?
• are COVID-19 related high dependency units (HDU) or intensive care units (ICU) admissions increasing at ≥25% over the same 7-day period?
• is COVID-19 related HDU or ICU occupancy increasing at ≥25% over the same 7-day period?
• are new daily COVID-19 related deaths increasing at ≥25% over the same 7-day period?
• is current direct COVID-19 absolute healthcare pressure sufficiently high to support escalation to level 4?

Rationale

Hospital activity and severe health outcomes are the key indicators representing healthcare pressures, but these will be subject to a lag from the point of infection. Hence the inclusion of transmission dynamics, doubling time and estimated incidence. Given the uncertainty in estimated incidence, a weekly case rate should also be considered.

Sources include laboratory test results, hospital admissions and death data (available on the GOV.UK dashboard). Estimated new infections will be informed by a range of sources, including survey data (for example Office for National Statistics (ONS) and ZOE/KCL) and mathematical modelling provided by SPI-M/SAGE.

Alert Level 5

There is a single holding indicator, with level 5 only recommended if that indicator is met:

• has UKHSA, in consultation with NHS senior leadership and CMOs, estimated that forecasted healthcare demand will outmatch forecasted capacity across the UK, regions or devolved administrations within the next 21 days?

Should the above indicator not be met, de-escalation to, or remain at, level 4 can be considered. This ensures that the focus remains on NHS capacity and operational pressures when COVID-19 infections are at high levels.

Rationale

A recommendation to escalate to COVID-19 alert level 5 should be made in consultation with health service directors and contingency planners, and should be based around their predicted capacity, which includes surge capacity and mutual aid. In principle, escalation to level 5 should allow sufficient time for the implementation of urgent national measures to protect healthcare services from being overwhelmed.

De-escalating from level 4 to level 3

Indicators:

• is the UK weekly case rate less than 125 per 100,000 population?
• is the national R reliably estimated to be <1?
• are there estimated to be less than 30,000 new infections per day?
• have new daily COVID-19 confirmed infections been on a downward trend, or stable at a low level, for at least 4 weeks?
• have COVID-19 related hospital admissions been on a downward trend, or stable at a low level, for at least 4 weeks?
• has COVID-19 related hospital occupancy been on a downward trend, or stable at a low level, for at least 4 weeks?
• have COVID-19 related HDU or ICU admissions been on a downward trend, or stable at a low level, for at least 4 weeks?
• has COVID-19 related HDU or ICU occupancy been on a downward trend, or stable at a low level, for at least 4 weeks?
• have new daily COVID-19 related deaths been on a downward trend, or stable at a low level, for at least 4 weeks?
• is current direct COVID-19 absolute healthcare pressure sufficiently low to support de-escalation to level 4?

Rationale

Estimated transmission dynamics of R<1 for a sustained period, combined with a demonstrable reduction in the number of people becoming severely unwell and/or dying, would give confidence that non-pharmaceutical interventions (or other controlling measures) have been effective.

Given the uncertainty in estimated incidence, and the fact that some estimates tended to lag when incidence was decreasing, a lower weekly case rate should also be considered to provide confidence that infections are decreasing.

Sources include laboratory test results, hospital admissions and death data (available on the GOV.UK dashboard), survey data (for example ONS and ZOE/KCL), and mathematical modelling provided by SPI-M/SAGE.

De-escalating from level 3 to 2

Indicators

• is the UK weekly case rate less than 25 per 100,000 population?
• have new daily COVID-19 confirmed infections been on a downward trend, or stable at a low level, for at least 4 weeks?
• have COVID-19 related hospital admissions been on a downward trend, or stable at a low level, for at least 4 weeks?
• has COVID-19 related hospital occupancy been on a downward trend, or stable at a low level, for at least 4 weeks?
• have new daily COVID-19 related deaths been on a downward trend, or stable at a low level, for at least 4 weeks?

Rationale

A 4-week declining trend gives confidence that transmission is declining, in addition to the falling new infection count.

Estimates of the number of new infections may be unstable at such low levels, or have very wide confidence intervals, hence the consideration of a weekly case rate alone.

Sources include laboratory test results, hospital admissions and death data (available on the GOV.UK dashboard), mathematical modelling provided by SPI-M/SAGE, and public health surveillance systems.

Thematic risk assessments

In addition to the above noted indicators, consideration is to be given to 2 primary thematic risks: variants and regional heterogeneity.

These 2 specific thematic areas have been selected due to their propensity to identify risks to the national alert level that may not otherwise have been captured by existing indicators, for example the emergence or spread of a variant with vaccine escape characteristics or a degree of regional heterogeneity that would be highly likely to lead to changes in national epidemiology in the short-term.

It is important to note that in exceptional circumstances a change to the alert level could be recommended based on thematic risk assessments alone, regardless of epidemic trajectory, and vice versa. This ensures that agile recommendations can be made, without waiting for predetermined indicators to be met.

Each thematic risk will be assessed as High, Medium, Low, or Minimal risk in terms of the propensity to have an impact on national alert level indicators in the short term.