Hospitalisation and mortality impact of shielding during 2020 in England: a transmission modelling evaluation using the OpenSAFELY platform

BackgroundDuring the early phase of the Covid-19 pandemic in England, people with pre-existing conditions that put them at severe clinical risk if infected were advised to drastically reduce face-to-face contacts in a policy known as "shielding". The impact of this policy in preventing COVID-19 hospitalisations and deaths has not been evaluated at the national level using transmission-dynamic modelling. MethodsWith the approval of NHS England, we present a retrospective cohort evaluation of the shielding policy, drawing data from electronic health records (EHRs) for 24 million patients in England accessed through the OpenSAFELY platform. The study is from 1 January to 1 December 2020, prior to vaccination and new SARS-CoV-2 variants. We used a dynamic transmission model of SARS-CoV-2 transmission, infection, and hospitalisation, stratified by age and shielding status for the general population (excluding care homes). We estimated transmission rates in the shielding and non-shielding groups using data from the CoMix social contact survey, and fitted the model to hospitalisations and deaths in and outside hospital. FindingsWe found that the risk of hospitalisation was higher for shielding people in all age groups and increased with age. The hospital fatality ratio was similar between shielding and non-shielding people from January to June 2020 and greater in shielding people from July 2020 onward. By comparing the observed epidemic to a counterfactual scenario without shielding, we projected that between 7800 and 10,600 hospitalisations and 2300 to 3500 deaths due to COVID-19 were directly averted by the policy, corresponding to reductions of 25% (24, 28%) and 23% (21, 25%), respectively, in the shielding population in England up to 1 December 2020. Including also the indirect effect in the non-shielding population, we projected between 14,700, and 21,800 hospitalisations and 3700 and 5500 deaths due to COVID-19 were averted by the policy in the total population, each corresponding to reductions of 13% (11, 16%). InterpretationBased on the data and assumptions in this study, the shielding policy reduced pressure on the NHS and severe illness and mortality in clinically-extremely vulnerable shielding patients in England up to 1 December 2020, and, through indirectly-reduced exposure, also in the non-shielding population. Similar policies for other infections could have a comparable public health impact in reducing both mortality and pressure on public health services. FundingMedical Research Foundation, Medical Research Council, National Institute for Health and Care Research, NHS England, The Wellcome Trust.