Relation of severe COVID-19 in Scotland to transmission-related factors and risk conditions eligible for shielding support: REACT-SCOT case-control study

Paul M. Mckeigue, David A. McAllister, David Caldwell, Ciara Gribben, Jen Bishop, Stuart McGurnaghan, Matthew Armstrong, Joke Delvaux, Sam Colville, Sharon Hutchinson, Chris Robertson, Nazir Lone, Jim McMenamin, David Goldberg, Helen M. Colhoun

Research output: Contribution to journalArticlepeer-review

9 Citations (Scopus)
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Background: Clinically vulnerable individuals have been advised to shield themselves during the COVID-19 epidemic. The objectives of this study were to investigate (1) the rate ratio of severe COVID-19 associated with eligibility for the shielding programme in Scotland across the first and second waves of the epidemic and (2) the relation of severe COVID-19 to transmission-related factors in those in shielding and the general population. Methods: Inamatchedcase-controldesign,all178,578diagnosedcasesofCOVID-19inScotlandfrom1March2020 to 18 February 2021 were matched for age, sex and primary care practice to 1,744,283 controls from the general population. This dataset (REACT-SCOT) was linked to the list of 212,702 individuals identified as eligible for shielding. Severe COVID-19 was defined as cases that entered critical care or were fatal. Rate ratios were estimated by conditional logistic regression.
Results: Withthosewithoutriskconditionsasreferencecategory,theunivariaterateratioforsevereCOVID-19was 3.21 (95% CI 3.01 to 3.41) in those with moderate risk conditions and 6.3 (95% CI 5.8 to 6.8) in those eligible for shielding. The highest rate was in solid organ transplant recipients: rate ratio 13.4 (95% CI 9.6 to 18.8). Risk of severe COVID-19 increased with the number of adults but decreased with the number of school-age children in the household. Severe COVID-19 was strongly associated with recent exposure to hospital (defined as 5 to 14 days before presentation date): rate ratio 12.3 (95% CI 11.5 to 13.2) overall. The population attributable risk fraction for recent exposure to hospital peaked at 50% in May 2020 and again at 65% in December 2020.
Conclusions: Theeffectivenessofshieldingvulnerableindividualswaslimitedbytheinabilitytocontroltransmission in hospital and from other adults in the household. Mitigating the impact of the epidemic requires control of nosocomial transmission.
Original languageEnglish
Article number149
Pages (from-to)1-13
Number of pages13
JournalBMC Medicine
Publication statusPublished - 23 Jun 2021


  • adult
  • COVID-19/complications
  • case-control studies
  • child
  • child, preschool
  • critical care
  • female
  • humans
  • logistic models
  • male
  • pregnancy
  • primary health care
  • risk factors
  • SARS-CoV-2
  • Scotland/epidemiology
  • nosocomial infection
  • transplant recipient
  • matched case control Studies
  • COVID-19/prevention and control

ASJC Scopus subject areas

  • Medicine(all)


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