Investigating the prevalence of long COVID in Scotland

Data and methodology

How to access the data

Previously published estimates of long COVID prevalence mentioned in this publication are available at:

• Prevalence of ongoing symptoms following coronavirus (COVID-19) infection in the UK - Office for National Statistics (ons.gov.uk)
• Self-reported coronavirus (COVID-19) infections and associated symptoms, England and Scotland - Office for National Statistics
• Scottish Health Survey - Scottish Government (www.gov.scot).

The full time series of the new estimates of long COVID prevalence presented in this publication, with further breakdowns by activity limitation and duration since first COVID-19 infection, are available in the supplementary data tables.

Methodology

The new analysis presented in this publication is a replication of the Office for National Statistics’ (ONS) prevalence of ongoing symptoms following COVID-19 infection in the UK analysis, using data from the Coronavirus (COVID-19) Infection Survey (CIS). The original ONS analysis was performed at UK-level, with limited breakdowns available at Scotland-level.

The only difference in method between the new analysis and the original ONS analysis is that, for the new analysis, responses were filtered to include participants in Scotland only.

The CIS pilot started in England in April 2020, with Scotland joining the survey in September 2020, and ran until March 2023. Questions asking participants about their experiences with long COVID were added to the CIS questionnaire in February 2021. Due to issues with the availability of historic data, the time period considered in the new analysis is the four-week period ending 4 April 2022 to 5 March 2023. Please note that data for the period ending 31 July 2022 has been excluded due to issues with data quality.

Due to changes in data collection mode from face-to-face interview to online, estimates up to and including the four-week period ending 2 July 2022 cannot be directly compared with estimates from the four-week period ending 3 September 2022 onwards. ONS undertook analysis (published in their September 2022 release) on the effects of the change in collection mode. They found that participants were 30% more likely to report long COVID remotely than they were face-to-face.

The previously published ONS estimates and the new estimates presented in this publication have accompanying 95% confidence intervals (see supplementary data tables). A confidence interval gives an indication of the degree of uncertainty around an estimate, with a wider interval indicating more uncertainty around the estimate. In this publication, a change in trend has been described as an increase or decrease, or differences between groups have been described as higher or lower, if the accompanying confidence intervals of the estimates being compared do not overlap.

In this publication, number estimates have been rounded to the nearest thousand and percentages rounded to the nearest one decimal place. More precise estimates can be found in the corresponding data sources, if available.

This work was undertaken in the ONS Secure Research Service (SRS) using data from ONS and other owners and does not imply the endorsement of the ONS or other data owners.

Limitations

Like all household surveys, not all sampled households invited to participate in the Coronavirus (COVID-19) Infection Survey enroll and individuals may drop out over time. The estimates are weighted to account for non-response. However, bias may be introduced if non-response is related to long COVID, for example, participants being more willing, or less able, to continue in the study because of their symptoms.

Long COVID status was self-reported by study participants and so misclassification is possible. For example, some participants may be experiencing symptoms because of a health condition unrelated to COVID-19 infection. Others who do have symptoms caused by COVID-19 may not describe themselves as experiencing long COVID (for example, because of lack of awareness of the term or not knowing they were initially infected with COVID-19).

References

Office for National Statistics; University of Oxford, released 03 April 2023, ONS SRS Metadata Catalogue, dataset, COVID-19 Infection Survey - UK, https://doi.org/10.57906/r47r-173.