{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,20]],"date-time":"2026-10-20T00:40:31Z","timestamp":1792456831120,"version":"4.5.0"},"reference-count":37,"publisher":"Oxford University Press (OUP)","issue":"6","license":[{"start":{"date-parts":[[2026,10,14]],"date-time":"2026-10-14T00:00:00Z","timestamp":1791936000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/academic.oup.com\/pages\/standard-publication-reuse-rights"}],"funder":[{"DOI":"10.13039\/501100004836","name":"Independent Research Fund Denmark","doi-asserted-by":"publisher","award":["3101-00013B"],"award-info":[{"award-number":["3101-00013B"]}],"id":[{"id":"10.13039\/501100004836","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":[],"published-print":{"date-parts":[[2026,10,14]]},"abstract":"<jats:title>Abstract<\/jats:title>\n                  <jats:sec>\n                    <jats:title>Background<\/jats:title>\n                    <jats:p>Transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) often clusters in families, suggesting role of shared environmental and genetic factors. We performed a nationwide Danish study of twins, their spouses, and matched population controls with the aim of disentangling the host genetic and environmental mechanisms underlying the familial clustering of SARS-CoV-2 susceptibility and coronavirus disease 2019 (COVID-19) severity.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Methods<\/jats:title>\n                    <jats:p>This registry-linkage study included 83\u00a0902 twins and 32\u00a0719 spouses, matched to 839\u00a0020 population controls and 327\u00a0190 spouse controls, respectively, and followed from 1 February 2020 to 31 October 2022. Testing positive for SARS-CoV-2 infection and COVID-19 hospitalization served as proxies for SARS-CoV-2 susceptibility and disease severity, respectively. We compared concordance rates and calculated heritability from biometrical modelling of these traits.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Results<\/jats:title>\n                    <jats:p>We found no evidence of a genetic influence on infection susceptibility in the first two waves of the pandemic and a modest influence [heritability: 19.4%; 95% confidence interval (CI): 10.0%\u201328.8%] in the third wave. Spouses showed the highest concordance rates by a large margin in all waves. Our study found no evidence of a genetic predisposition to disease severity. Co-twins of hospitalized twins had no increased risk of hospitalization. By contrast, the risk of being hospitalized with COVID-19 was higher [relative risk: 3.56; 95% CI: 2.57\u20134.92] among the spouses of the hospitalized twins than among the controls.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Conclusion<\/jats:title>\n                    <jats:p>Social proximity was a key determinant of infection susceptibility. A three-fold increased risk for spouses suggests that viral load and lifestyle shared between spouses were more important determinants of severe COVID-19 than genetic susceptibility.<\/jats:p>\n                  <\/jats:sec>","DOI":"10.1093\/ije\/dyag204","type":"journal-article","created":{"date-parts":[[2026,10,20]],"date-time":"2026-10-20T00:03:08Z","timestamp":1792454588000},"source":"Crossref","is-referenced-by-count":0,"title":["Familial factors in SARS-CoV-2 susceptibility and COVID-19 severity: a nationwide Danish study of adult twins and their spouses"],"prefix":"10.1093","volume":"55","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-2503-4253","authenticated-orcid":false,"given":"Maria N","family":"Timofeeva","sequence":"first","affiliation":[{"name":"The Epidemiology, Biostatistics and Biodemography Research Unit, Department of Public Health, University of Southern Denmark , Odense,","place":["Denmark"]},{"name":"The Danish Twin Registry, Department of Public Health, University of Southern Denmark , Odense,","place":["Denmark"]},{"name":"Danish Institute for Advanced Study, University of Southern Denmark , Odense,","place":["Denmark"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Jacob Krabbe","family":"Pedersen","sequence":"additional","affiliation":[{"name":"The Epidemiology, Biostatistics and Biodemography Research Unit, Department of Public Health, University of Southern Denmark , Odense,","place":["Denmark"]},{"name":"The Danish Twin Registry, Department of Public Health, University of Southern Denmark , Odense,","place":["Denmark"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Dorthe Almind","family":"Pedersen","sequence":"additional","affiliation":[{"name":"The Epidemiology, Biostatistics and Biodemography Research Unit, Department of Public Health, University of Southern Denmark , Odense,","place":["Denmark"]},{"name":"The Danish Twin Registry, Department of Public Health, University of Southern Denmark , 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