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.
- COVID-19/prevention and control, transplant recipient, nosocomial infection, matched case control studies