{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,31]],"date-time":"2026-10-31T11:27:22Z","timestamp":1793446042272,"version":"4.5.0"},"reference-count":26,"publisher":"Oxford University Press (OUP)","issue":"4","license":[{"start":{"date-parts":[[2025,6,19]],"date-time":"2025-06-19T00:00:00Z","timestamp":1750291200000},"content-version":"vor","delay-in-days":8,"URL":"https:\/\/creativecommons.org\/licenses\/by-nc-nd\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100000805","name":"European Centre for Disease Prevention and Control","doi-asserted-by":"publisher","id":[{"id":"10.13039\/501100000805","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":[],"published-print":{"date-parts":[[2025,6,11]]},"abstract":"<jats:title>Abstract<\/jats:title>\n               <jats:sec>\n                  <jats:title>Background<\/jats:title>\n                  <jats:p>With SARS-CoV-2 self-tests, persons with acute respiratory infections (ARI) can know their COVID-19 status. This may alter their decision to consult a general practitioner (GP), potentially biasing COVID-19 vaccine effectiveness (VE) studies. We explore bias mechanisms, simulate magnitude, and verify control methods.<\/jats:p>\n               <\/jats:sec>\n               <jats:sec>\n                  <jats:title>Methods<\/jats:title>\n                  <jats:p>We used directed acyclic graphs (DAGs) to illustrate the bias mechanisms. Based on the European primary care VEBIS multicentre test-negative design (TND) study, we simulated populations with varying true VE (20%\u201360%), proportions of persons with ARI self-testing (10%\u201330%), effect of COVID-19 vaccination on self-testing (1.5\u20132.5), and effect of self-test result on GP consultation (0.5\u20132). We performed 5000 runs per scenario, estimating VE among those consulting a GP. We calculated bias as true VE minus mean simulated VE, unadjusted and adjusted for self-testing, using logistic regression.<\/jats:p>\n               <\/jats:sec>\n               <jats:sec>\n                  <jats:title>Results<\/jats:title>\n                  <jats:p>DAGs suggested collider stratification bias if vaccination had an effect on self-testing and if self-test results affected GP consultation. Bias was \u221212% to 18% at 20% true VE, with the most extreme associations and 30% self-testing. With 60% true VE and 10%\u201320% self-testing, bias was lower. Bias was higher (\u221218% to 45%) if both positive and negative self-test results affected GP consultation. Adjusting for self-testing removed the bias.<\/jats:p>\n               <\/jats:sec>\n               <jats:sec>\n                  <jats:title>Conclusions<\/jats:title>\n                  <jats:p>Self-testing may bias COVID-19 VE TND studies in primary care if self-testing is high, particularly with low VE. We recommend primary care TND VE studies collect self-testing information to eliminate potential bias. Observational studies are needed to understand the relationship between vaccination, self-testing, and GP consultation, in these studies\u2019 source population.<\/jats:p>\n               <\/jats:sec>","DOI":"10.1093\/ije\/dyaf086","type":"journal-article","created":{"date-parts":[[2025,6,27]],"date-time":"2025-06-27T18:10:46Z","timestamp":1751047846000},"source":"Crossref","is-referenced-by-count":10,"title":["The potential bias introduced into COVID-19 vaccine effectiveness studies at primary care level due to the availability of SARS-CoV-2 tests in the general population"],"prefix":"10.1093","volume":"54","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-7038-325X","authenticated-orcid":false,"given":"Charlotte","family":"Lani\u00e8ce Delaunay","sequence":"first","affiliation":[{"name":"Epidemiology Department, Epiconcept , Paris,","place":["France"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Baltazar","family":"Nunes","sequence":"additional","affiliation":[{"name":"Epidemiology Department, Epiconcept , Paris,","place":["France"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Susana","family":"Monge","sequence":"additional","affiliation":[{"name":"Department of Communicable Diseases, National Centre of Epidemiology, Institute of Health Carlos III , Madrid,","place":["Spain"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Marit","family":"de Lange","sequence":"additional","affiliation":[{"name":"Centre for Infectious Disease Control, National Institute for Public Health and the Environment , Bilthoven,","place":["The 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Stockholm,","place":["Sweden"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0009-0008-8546-6331","authenticated-orcid":false,"given":"Ivan","family":"Mlinari\u0107","sequence":"additional","affiliation":[{"name":"Division for Epidemiology of Communicable Diseases, Croatian Institute of Public Health , Zagreb,","place":["Croatia"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Mihaela","family":"Lazar","sequence":"additional","affiliation":[{"name":"National Influenza Centre, Cantacuzino National Military-Medical Institute for Research and Development , Bucharest,","place":["Romania"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Paloma","family":"Botella Rocamora","sequence":"additional","affiliation":[{"name":"Subdirecci\u00f3 General d\u2019Epidemiologia i Vigil\u00e0ncia de la Salut, Direcci\u00f3 General de Salut P\u00fablica, Generalitat Valenciana , Valencia,","place":["Spain"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Annika","family":"Erdwiens","sequence":"additional","affiliation":[{"name":"Department for Infectious Disease Epidemiology, Respiratory Infections Unit, Robert Koch Institute , Berlin,","place":["Germany"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"No\u00e9mie","family":"S\u00e8ve","sequence":"additional","affiliation":[{"name":"Sorbonne Universit\u00e9, INSERM, Institut Pierre Louis d'\u00e9pid\u00e9miologie et de Sant\u00e9 Publique (IPLESP) , Paris,","place":["France"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Lisa","family":"Domegan","sequence":"additional","affiliation":[{"name":"Health Service Executive-Health Protection Surveillance Centre , Dublin,","place":["Ireland"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Iv\u00e1n","family":"Mart\u00ednez-Baz","sequence":"additional","affiliation":[{"name":"Instituto de Salud 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