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Secondary outcomes included additional prioritised adverse events of special interest. Poisson regression was used to estimate incidence rate ratios with adjustment for selected covariates.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Results<\/jats:title>\n                    <jats:p>Individuals who had had a heterologous primary vaccine (n=137 495) or a homologous vaccine (n=2 688 142) were identified, in addition to those who had had a heterologous booster (n=129 770) or a homologous booster (n=2 197 213). Adjusted incidence rate ratios of adverse cardiovascular and haemostatic events within 28 days for the heterologous primary and booster vaccine schedules in comparison with the homologous mRNA vaccine schedules were 1.22 (95% confidence interval 0.79 to 1.91) and 1.00 (0.58 to 1.72) for ischaemic cardiac events, 0.74 (0.40 to 1.34) and 0.72 (0.37 to 1.42) for cerebrovascular events, 1.12 (0.13 to 9.58) and 4.74 (0.94 to 24.01) for arterial thromboembolisms, 0.79 (0.45 to 1.38) and 1.09 (0.60 to 1.98) for venous thromboembolisms, 0.84 (0.18 to 3.96) and 1.04 (0.60 to 4.55) for myocarditis or pericarditis, 0.97 (0.45 to 2.10) and 0.89 (0.21 to 3.77) for thrombocytopenia and coagulative disorders, and 1.39 (1.01 to 1.91) and 1.02 (0.70 to 1.47) for other bleeding events, respectively. No associations with any of the outcomes were found when restricting to serious adverse events defined as stay in hospital for more than 24 h.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Conclusion<\/jats:title>\n                    <jats:p>Heterologous primary and booster covid-19 vaccine schedules of ChAdOx1-S priming and mRNA booster doses as both second and third doses were not associated with increased risk of serious adverse events compared with homologous mRNA vaccine schedules. These results are reassuring but given the rarity of some of the adverse events, associations cannot be excluded.<\/jats:p>\n                  <\/jats:sec>","DOI":"10.1136\/bmj-2022-070483","type":"journal-article","created":{"date-parts":[[2022,7,13]],"date-time":"2022-07-13T09:45:11Z","timestamp":1657705511000},"page":"e070483","update-policy":"https:\/\/doi.org\/10.1136\/crossmarkpolicy","source":"Crossref","is-referenced-by-count":10,"title":["Safety of heterologous primary and booster schedules with ChAdOx1-S and BNT162b2 or mRNA-1273 vaccines: nationwide cohort study"],"prefix":"10.1136","volume":"378","author":[{"ORCID":"https:\/\/orcid.org\/0000-0001-7622-6303","authenticated-orcid":false,"given":"Niklas Worm","family":"Andersson","sequence":"first","affiliation":[{"name":"Department of Epidemiology Research, Statens Serum Institut, Copenhagen, Denmark"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Emilia Myrup","family":"Thiesson","sequence":"additional","affiliation":[{"name":"Department of Epidemiology Research, Statens Serum Institut, Copenhagen, Denmark"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Mona Vestergaard","family":"Laursen","sequence":"additional","affiliation":[{"name":"Data Analytics Centre, Danish Medicines Agency, Copenhagen, Denmark"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Stine Hasling","family":"Mogensen","sequence":"additional","affiliation":[{"name":"Data Analytics Centre, Danish Medicines Agency, Copenhagen, Denmark"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Jesper","family":"Kj\u00e6r","sequence":"additional","affiliation":[{"name":"Data Analytics Centre, Danish Medicines Agency, Copenhagen, Denmark"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Anders","family":"Hviid","sequence":"additional","affiliation":[{"name":"Department of Epidemiology Research, Statens Serum Institut, Copenhagen, Denmark"},{"name":"Pharmacovigilance Research Center, Department of Drug Development and Clinical Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"239","published-online":{"date-parts":[[2022,7,13]]},"reference":[{"key":"2025110101562936000_378.jul13_14.e070483.1","doi-asserted-by":"publisher","DOI":"10.1056\/NEJMoa2104840"},{"key":"2025110101562936000_378.jul13_14.e070483.2","doi-asserted-by":"publisher","DOI":"10.1056\/NEJMoa2104882"},{"key":"2025110101562936000_378.jul13_14.e070483.3","doi-asserted-by":"publisher","DOI":"10.1136\/bmj.n699"},{"key":"2025110101562936000_378.jul13_14.e070483.4","unstructured":"European Centre for Disease Prevention and Control. 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