Objective To assess rates of cardiovascular and haemostatic events in the first 28 days after vaccination with the Oxford-AstraZeneca vaccine ChAdOx1-S in Denmark and Norway and to compare them with rates observed in the general populations. Design Population based cohort study. Setting Nationwide healthcare registers in Denmark and Norway. Participants All people aged 18-65 years who received a first vaccination with ChAdOx1-S from 9 February 2021 to 11 March 2021. The general populations of Denmark (2016-18) and Norway (2018-19) served as comparator cohorts. Main outcome measures Observed 28 day rates of hospital contacts for incident arterial events, venous thromboembolism, thrombocytopenia/coagulation disorders, and bleeding among vaccinated people compared with expected rates, based on national age and sex specific background rates from the general populations of the two countries. Results The vaccinated cohorts comprised 148 792 people in Denmark (median age 45 years, 80% women) and 132 472 in Norway (median age 44 years, 78% women), who received their first dose of ChAdOx1-S. Among 281 264 people who received ChAdOx1-S, the standardised morbidity ratio for arterial events was 0.97 (95% confidence interval 0.77 to 1.20). 59 venous thromboembolic events were observed in the vaccinated cohort compared with 30 expected based on the incidence rates in the general population, corresponding to a standardised morbidity ratio of 1.97 (1.50 to 2.54) and 11 (5.6 to 17.0) excess events per 100 000 vaccinations. A higher than expected rate of cerebral venous thrombosis was observed: standardised morbidity ratio 20.25 (8.14 to 41.73); an excess of 2.5 (0.9 to 5.2) events per 100 000 vaccinations. The standardised morbidity ratio for any thrombocytopenia/coagulation disorders was 1.52 (0.97 to 2.25) and for any bleeding was 1.23 (0.97 to 1.55). 15 deaths were observed in the vaccine cohort compared with 44 expected. Conclusions Among recipients of ChAdOx1-S, increased rates of venous thromboembolic events, including cerebral venous thrombosis, were observed. For the remaining safety outcomes, results were largely reassuring, with slightly higher rates of thrombocytopenia/coagulation disorders and bleeding, which could be influenced by increased surveillance of vaccine recipients. The absolute risks of venous thromboembolic events were, however, small, and the findings should be interpreted in the light of the proven beneficial effects of the vaccine, the context of the given country, and the limitations to the generalisability of the study findings.

中文翻译：

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丹麦和挪威的牛津-阿斯利康ChAdOx1-S疫苗接种后的动脉事件，静脉血栓栓塞，血小板减少和出血：基于人群的队列研究

目的评估牛津-阿斯利康疫苗ChAdOx1-S在丹麦和挪威接种后头28天的心血管和止血事件发生率，并将其与普通人群中观察到的发生率进行比较。设计基于人群的队列研究。在丹麦和挪威设立全国性的医疗保健机构。参与者从2021年2月9日至2021年3月11日接受ChAdOx1-S首次疫苗接种的所有18-65岁人群。丹麦（2016-18）和挪威（2018-19）的总人口作为比较人群。主要结局指标观察到与接种率相比，接种疫苗的人发生动脉事件，静脉血栓栓塞，血小板减少/凝血功能障碍和出血的医院联系28天的发生率，根据两国总人口的民族年龄和性别背景比率得出。结果接种疫苗的人群包括丹麦的148 792人（中年年龄45岁，女性80％）和挪威的132 472人（中年年龄44岁，女性78％），他们接受了第一剂ChAdOx1-S。在接受ChAdOx1-S的281264人中，动脉事件的标准发病率为0.97（95％置信区间为0.77至1.20）。接种人群中观察到59例静脉血栓栓塞事件，相比之下，根据普通人群的发病率预计有30例，对应于每10万人接种的标准发病率1.97（1.50至2.54）和11例（5.6至17.0）超标事件。观察到的脑静脉血栓形成率高于预期：标准发病率20.25（8.14至41。73）；每10万次接种超过2.5（0.9到5.2）个事件。任何血小板减少/凝血障碍的标准发病率是1.52（0.97至2.25），而任何出血则是1.23（0.97至1.55）。在疫苗队列中观察到15例死亡，而预期为44例。结论在ChAdOx1-S的接受者中，观察到静脉血栓栓塞事件（包括脑静脉血栓形成）的发生率增加。对于其余的安全结果，结果在很大程度上令人放心，血小板减少症/凝血功能障碍和出血的发生率略高，这可能受疫苗接种者监测的增加所影响。但是，静脉血栓栓塞事件的绝对风险很小，应根据已证实的疫苗有益作用来解释这一发现，