Background Excess mortality captures the total effect of the Coronavirus Disease 2019 (COVID-19) pandemic on mortality and is not affected by misspecification of cause of death. We aimed to describe how health and demographic factors were associated with excess mortality during, compared to before, the pandemic. Methods and findings We analysed a time series dataset including 9,635,613 adults (≥40 years old) registered at United Kingdom general practices contributing to the Clinical Practice Research Datalink. We extracted weekly numbers of deaths and numbers at risk between March 2015 and July 2020, stratified by individual-level factors. Excess mortality during Wave 1 of the UK pandemic (5 March to 27 May 2020) compared to the prepandemic period was estimated using seasonally adjusted negative binomial regression models. Relative rates (RRs) of death for a range of factors were estimated before and during Wave 1 by including interaction terms. We found that all-cause mortality increased by 43% (95% CI 40% to 47%) during Wave 1 compared with prepandemic. Changes to the RR of death associated with most sociodemographic and clinical characteristics were small during Wave 1 compared with prepandemic. However, the mortality RR associated with dementia markedly increased (RR for dementia versus no dementia prepandemic: 3.5, 95% CI 3.4 to 3.5; RR during Wave 1: 5.1, 4.9 to 5.3); a similar pattern was seen for learning disabilities (RR prepandemic: 3.6, 3.4 to 3.5; during Wave 1: 4.8, 4.4 to 5.3), for black or South Asian ethnicity compared to white, and for London compared to other regions. Relative risks for morbidities were stable in multiple sensitivity analyses. However, a limitation of the study is that we cannot assume that the risks observed during Wave 1 would apply to other waves due to changes in population behaviour, virus transmission, and risk perception. Conclusions The first wave of the UK COVID-19 pandemic appeared to amplify baseline mortality risk to approximately the same relative degree for most population subgroups. However, disproportionate increases in mortality were seen for those with dementia, learning disabilities, non-white ethnicity, or living in London. Helen Strongman and colleagues investigate the health and demographic factors associated with excess mortality during, as compared to before, the COVID-19 pandemic. Author summary Why was this study done? All-cause mortality during the Coronavirus Disease 2019 (COVID-19) pandemic was substantially higher than in previous years, particularly among elderly people, males, people of non-white ethnicity, people of lower socioeconomic status, and people living in care homes. There is little evidence of how preexisting health and demographic factors are associated with all-cause mortality and how this compares to mortality risks in people with and without these factors before the pandemic. What did the researchers do and find? We used seasonally adjusted time series models to estimate all-cause and excess mortality during Wave 1 of the UK pandemic (5 March to 27 May 2020) for people with individual health and sociodemographic factors; we then estimated relative risks of all-cause mortality in people with and without these factors before the pandemic and during Wave 1. We found similar relative risks of all-cause mortality in people with and without each factor before and during Wave 1 of the pandemic, but there were exceptions. Health-related exceptions were people with a diagnosis of dementia or learning disabilities, whose risk of death relative to people without these conditions was substantially higher during Wave 1 than it was before the pandemic. Socioeconomic exceptions were non-white ethnicity and living in London; these groups had lower immediate risks of death before the pandemic compared to white people or people living outside of London, but substantially elevated relative risks during Wave 1. What do these findings mean? This suggests that COVID-19 has dialled up the risk of death by a similar proportional degree for most people. From a clinical perspective, prepandemic knowledge about the relative frailty associated with different conditions can be reasonably applied in the pandemic situation, though further follow-up will be needed to confirm that our observations generalise beyond Wave 1. Exceptions include people with learning difficulties and dementia who may have been more exposed to infection in care homes and through personal care and those of non-white ethnicity who may have been at higher risk due to increased social interactions.
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