Coronavirus and clinically extremely vulnerable people in England methodology

The COVID High Risk Group Insights Study was compiled in response to policy questions on whether the population who had been advised to shield were following the guidance issued for clinically extremely vulnerable people, and the impact it had on their well-being and behaviours. The survey was produced, run, and analysed in a collaboration between the Department for Health and Social Care (DHSC), NHS Digital (NHS-D) and the Office for National Statistics (ONS).

This survey was specifically designed to obtain information on the people advised by the government to shield from the coronavirus (COVID-19). As with all surveys, the estimates included in this bulletin have an associated margin of error. The ONS experts were consulted on questionnaire design.

Methodological information

The survey respondents were selected using implicit stratification from a list of those identified as clinically extremely vulnerable (CEV) and were contacted by telephone.

In waves one and two, the estimates were weighted to adjust for:

• sex
• age group (16 to 17 years, 18 to 29 years, 30 to 39 years, 40 to 49 years, 50 to 59 years, 60 to 69 years, 70 to 79 years, 80 to 89 years, 90 years and over)

In waves three to six , the estimates were weighted to adjust for:

• whether the CEV person was identified as CEV through their clinical condition or clinician's review, or by the COVID-19 population risk assessment
• sex
• age group (under 65 years or 65 years and over)

In wave seven, the estimates were weighted to adjust for:

• sex
• age group (under 65 years or 65 years and over)

All answers are self-reported. Family members or carers may respond on behalf of those they care for where appropriate, for example, those unable to answer themselves.

Changes in the shielding population from 15 February 2021

In February 2021, an additional 1.5 million people were identified as being CEV. For more information on this, please see Identifying clinically extremely vulnerable people.

Changes to the shielding guidance from 1 April 2021

The national advice given to CEV people to shield paused on 31 March 2021. From 1 April 2021 until 15 September 2021, CEV people were issued precautionary guidance in addition to any national restrictions in place.

Changes to the shielding guidance from 15 September 2021

The national shielding advice given to people previously considered CEV ended on 15 September 2021. The new guidance suggests that people previously considered CEV should consider advice from their health professional on whether additional precautions could be right for them. The latest guidance was published on 28 September 2021 and is available at Guidance on shielding and protecting people who are clinically extremely vulnerable from COVID-19.

Changes to the questionnaire between waves

Questions have been improved or removed based on testing and analysis, and to ensure they align with government updates surrounding guidance for people who have been identified as CEV.

Differences between shielding and other stay at home guidance

Shielding differs from guidance for self-isolation (self-quarantine because either a person or someone in their household displays symptoms or receives a positive COVID-19 test result) and guidance for social distancing (measures everyone should be taking to reduce social interaction with other households). Shielding advice (given between January and March 2021) was for clinically extremely vulnerable people to stay in their house or garden with no visitors, except in the following circumstances:

• having visitors for support with personal care of themselves or someone in the household
• interacting with their support bubble, if they were eligible to form one
• leaving the house for exercise
• leaving the house for medical appointments

At the start of the coronavirus (COVID-19) pandemic, some members of the public were identified as being at high risk of severe illness from COVID-19. This list has been updated continually and the number identified as clinically extremely vulnerable (CEV) remained stable at 2.2 million people until February 2021. In February 2021, a further 1.5 million people were identified as CEV following the COVID-19 population risk assessment. More information can be found in Guidance on shielding and protecting people who are CEV from COVID-19.

Those who were identified as CEV in February 2021 by the COVID-19 population risk assessment were contacted by letter that month and advised to shield. Shielding was a voluntary action.

CEV people were informed in March 2021 that from 1 April 2021 they were no longer advised to shield. In the letter sent [PDF, 204KB], it explained that despite no longer being advised to shield, it was recommended they take extra precautions to protect themselves while COVID-19 is still spreading within communities.

From 15 September 2021, people previously considered to be CEV were informed that the shielding programme had ended in England. In the letter sent [PDF, 83KB], it explained they should continue to follow the same general guidance as everyone else and they may want to think about extra ways to keep themselves and others safe.

The main strengths of the COVID High Risk Group Insights Study include:

• the survey is a unique source of data for many uses
• the quick turnaround between finalising the questions and delivering the outputs allows for the timely production of data and statistics that can respond quickly to changing needs
• the questions asked to respondents are reviewed for each wave, enabling the survey to be adapted to reflect changes in guidance set by the government
• the sample was stratified by sex, age and region to be representative of the population being sampled
• the sample was weighted by characteristics to account for non-response bias, ensuring that the analysis was representative of the CEV population
• quality assurance procedures are undertaken throughout the analysis stages to minimise the risk of error

The main limitations of the COVID High Risk Group Insights Study include:

• in the case of those who are unable to answer the survey themselves, other people (for example, a family member or carer) can answer on their behalf; in this wave of the survey, those responding on behalf of the clinically extremely vulnerable (CEV) person were not asked about well-being and attitudes
• because of the introduction of new groups identified as CEV by the COVID-19 population risk assessment in February 2021, there is limited comparability between waves one and two with wave three and future waves of the survey
• changes made over time to both the questionnaire design and to the shielding guidance limit the range of time series analysis that can be conducted across waves
• as with all surveys these estimates have an associated margin of error, as they are based on a sample of CEV people, which is weighted to be representative of the whole CEV population