The impact of shielding on COVID-19 hospitalisations and deaths during 2020 in England: a transmission modelling...

During the early phase of the COVID-19 pandemic in England, people with pre-existing conditions at severe clinical risk were advised to drastically reduce face-to-face contacts in a policy known as "shielding". The impact of shielding in preventing COVID-19 hospitalisations and deaths has not been evaluated nationally using transmission-dynamic modelling.

With 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-1 December 2020, prior to vaccination and SARS-CoV-2 variants. We used a dynamic 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.

We found the risk of hospitalisation was higher for shielding people at all ages and increased with age. The hospitalisation fatality risk 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 14,700 - 21,800 hospitalisations and 3700-5500 deaths due to COVID-19 were averted by the policy in the total population, each corresponding to reductions of 13% (11, 16%).

Based on our data and assumptions, we estimated the shielding policy reduced 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 health services.