Background: Although COVID-19 vaccines have been shown to have high efficacy in the general population, it has not been established whether this applies to vulnerable groups. The objective of this study was to estimate the efficacy of vaccination in reducing the risk of severe COVID-19 among those designated as clinically extremely vulnerable in Scotland.

Methods: In a matched case-control design (REACT-SCOT), all 111295 cases of COVID-19 in Scotland diagnosed from 1 December 2020 to 16 March 2021 were matched for age, sex and primary care practice to 1093449 controls from the general population. This was linked to national data on vaccinations and those designated as clinically extremely vulnerable and thus eligible for shielding support. Severe COVID-19 was defined as cases with entry to critical care or fatal outcome. Rate ratios associated with vaccination within risk groups were estimated by conditional logistic regression.

Results: The rate ratio for severe COVID-19 associated with vaccination at least 14 days before was 0.29 (95% CI 0.22 to 0.37) in those eligible for shielding, compared with 0.29 (95% CI 0.25 to 0.34) in those ineligible for shielding. The rate ratio for hospitalized or fatal COVID-19 was 0.39 (95% CI 0.33 to 0.46) in those eligible and 0.37 (95% CI 0.33 to 0.41) in those not eligible for shielding. Examined by specific shielding conditions, the rate ratio for hospitalized or fatal COVID-19 ranged from 0.33 (95% CI 0.21 to 0.51) in those with specific cancers to 0.74 (95% CI 0.36 to 1.51) in solid organ transplant recipients, and 0.53 (95% CI 0.33 to 0.84) in others on immunosuppressants (excluding solid organ transplant recipients).

Conclusions: These results are reassuring with respect to efficacy in clinically vulnerable individuals including immunocompromised individuals, but studies in larger populations are needed to estimate efficacy in solid organ transplant recipients.


This is an open access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Cite as

McKeigue, P., McAllister, D., Bishop, J., Hutchinson, S., Robertson, C., Lone, N., McMenamin, J., Goldberg, D. & Colhoun, H. 2021, 'Efficacy of COVID-19 vaccination in individuals designated as clinically extremely vulnerable in Scotland'. To be published in F1000Research [Preprint]. Available at: https://doi.org/10.12688/f1000research.53812.1

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Last updated: 17 September 2022
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