Ethnic disparities in COVID-19: increased risk of infection or severe disease? – Authors' reply
Authors: Rohini Mathur, Christopher T Rentsch, Caroline E Morton, Rosalind M Eggo, Krishnan Bhaskaran, Laurie Tomlinsonn, Liam Smeeth, Ben Goldacre
Journal: The Lancet (2021)

We thank Daniel Pan and colleagues for raising an important point regarding our cohort study.1Mathur R Rentsch CT Morton CE et al.Ethnic differences in SARS-CoV-2 infection and COVID-19-related hospitalisation, intensive care unit admission, and death in 17 million adults in England: an observational cohort study using the OpenSAFELY platform.Lancet. 2021; 397: 1711-1724Summary Full Text Full Text PDF PubMed Scopus (262) Google Scholar We agree that separating the risk of infection from the risk of severe disease among those infected is a key issue in understanding and tackling ethnic disparities in COVID-19.2Mathur R Bear L Khunti K Eggo RM Urgent actions and policies needed to address COVID-19 among UK ethnic minorities.Lancet. 2020; 396: 1866-1868Summary Full Text Full Text PDF PubMed Scopus (24) Google Scholar Separating these risks in routine electronic health data sources is challenging. During the first wave of the pandemic in the UK, testing for SARS-CoV-2 was not random, with prioritisation of health-care workers and those admitted to hospital. Although testing was more common during the second wave, those receiving a test were still not entirely representative of the population infected with SARS-CoV-2. Indeed, in our own study, we found that minority ethnic groups were less likely to be tested for SARS-CoV-2 than White groups were in the second wave.1Mathur R Rentsch CT Morton CE et al.Ethnic differences in SARS-CoV-2 infection and COVID-19-related hospitalisation, intensive care unit admission, and death in 17 million adults in England: an observational cohort study using the OpenSAFELY platform.Lancet. 2021; 397: 1711-1724Summary Full Text Full Text PDF PubMed Scopus (262) Google Scholar Therefore restricting our analyses of severe COVID-19 outcomes to those who tested positive for SARS-CoV-2 could have introduced bias and limited interpretation of the resulting estimates.3Griffith GJ Morris TT Tudball MJ et al.Collider bias undermines our understanding of COVID-19 disease risk and severity.Nat Commun. 2020; 115749Crossref PubMed Scopus (449) Google Scholar To generate unbiased estimates of ethnic differences in COVID-19 severity among those infected, we would have needed to be confident that uptake of testing in relation to infection prevalence was equivalent between ethnic groups at the point of analysis. Alternatively, we would have needed to adjust for all factors associated with testing positive for SARS-CoV-2,3Griffith GJ Morris TT Tudball MJ et al.Collider bias undermines our understanding of COVID-19 disease risk and severity.Nat Commun. 2020; 115749Crossref PubMed Scopus (449) Google Scholar including occupation,4Pouwels KB House T Pritchard E et al.Community prevalence of SARS-CoV-2 in England from April to November, 2020: results from the ONS Coronavirus Infection Survey.Lancet Public Health. 2021; 6: e30-e38Summary Full Text Full Text PDF PubMed Scopus (92) Google Scholar which is not captured in routine electronic health data. Our study provides other clues that ethnic differences in severe COVID-19 outcomes might be driven by exposure risk, including the attenuation of risk on adjustment for household size and the rapid change in ethnic patterning of outcomes from the first wave to the second wave, which would be unlikely if ethnic differences were more related to the effects of underlying susceptibility than to increased exposure. There are now a number of population-based cohorts in the UK, within which it might be possible to reliably estimate COVID-19 severity in a representative sample of people with known infection. These include the REACT-2 study, which has already reported higher levels of SARS-CoV-2 antibodies in minority ethnic groups but no ethnic differences in infection-to-mortality ratios.5Ward H Atchison C Whitaker M et al.SARS-CoV-2 antibody prevalence in England following the first peak of the pandemic.Nat Commun. 2021; 12: 905Crossref PubMed Scopus (121) Google Scholar Studies from the Office for National Statistics and the UK Biobank highlighting the role of occupational exposure in COVID-19 mortality further support the hypothesis that ethnic differences in severe COVID-19 outcomes might be related to differences in exposure risk rather than other explanations, such as biological differences or health-care related factors.6Nafilyan V Pawelek P Ayoubkhani D et al.Occupation and COVID-19 mortality in England: a national linked data study of 14·3 million adults.medRxiv. 2021; (published online May 17.) (preprint).https://doi.org/10.1101/2021.05.12.21257123Google Scholar, 7Mutambudzi M Niedwiedz C Macdonald EB et al.Occupation and risk of severe COVID-19: prospective cohort study of 120 075 UK Biobank participants.Occup Environ Med. 2020; 78: 307-314Crossref PubMed Scopus (339) Google Scholar We look forward to findings from ongoing prospective cohort studies, which will build upon existing insights from sociological and community engagement work to disentangle the complex interactions between ethnicity, social disadvantage, occupational and household factors, and access to health care in explaining health inequalities related to COVID-19 and beyond.8Scientific Advisory Group for Emergencies (SAGE) COVID-19 Ethnicity subgroupInterpreting differential health outcomes among minority ethnic groups in wave 1 and 2.https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/976030/S1168_Ethnicity_Subgroup_Wave_1_and_2_qual_comparison.pdfDate: April 9, 2021Date accessed: May 2, 2021Google Scholar RM reports research funding from the Wellcome Trust and personal fees from AMGEN, unrelated to this Correspondence. All other authors declare no competing interests. Ethnic differences in SARS-CoV-2 infection and COVID-19-related hospitalisation, intensive care unit admission, and death in 17 million adults in England: an observational cohort study using the OpenSAFELY platformSome minority ethnic populations in England have excess risks of testing positive for SARS-CoV-2 and of adverse COVID-19 outcomes compared with the White population, even after accounting for differences in sociodemographic, clinical, and household characteristics. Causes are likely to be multifactorial, and delineating the exact mechanisms is crucial. Tackling ethnic inequalities will require action across many fronts, including reducing structural inequalities, addressing barriers to equitable care, and improving uptake of testing and vaccination. Full-Text PDF Open AccessEthnic disparities in COVID-19: increased risk of infection or severe disease?Rohini Mathur and colleagues found that Black and Asian ethnic groups were more likely to have adverse COVID-19 outcomes compared with the White population, even after accounting for differences in sociodemographic, clinical, and household characteristics.1 These findings are timely and striking, in light of the Commission on Race and Ethnic Disparities' recent report,2 which has been criticised for suggesting that the "claim the country is still institutionally racist is not borne out of evidence". Full-Text PDF