Arterial events, venous thromboembolism, thrombocytopenia, and bleeding after vaccination with Oxford-AstraZeneca ChAdOx1-S in Denmark and Norway: population based cohort study

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• Study Design

• Country of Study

• Level of Evidence

• Aim/ Question studied

• To compare rates of cardiovascular and haemostatic events in Denmark and Norway in the first 28 days after vaccination with the Oxford-AstraZeneca vaccine ChAdOx1-S to rates observed in the general population.

• Study done / What did they do?

• In this large binational cohort study, They observed 28-day rates of hospital contacts for incident arterial events, venous thromboembolism, thrombocytopenia/coagulation disorders, and bleeding among vaccinated people were compared to expected rates based on national age and sex specific background rates from the two countries’ general populations.

• The standardised morbidity ratio for arterial events was 0.97 among 281 264 people who received ChAdOx1-S, and 59 venous thromboembolic events were observed in the vaccinated cohort compared to 30 expected based on the incidence rates in the general population, corresponding to a standardised morbidity ratio of 1.97 and 11 excess events per 100 000 vaccinations. 
• The rate of cerebral venous thrombosis was higher than expected.

• Conclusion

The results of the safety outcomes were mostly reassuring, with slightly higher rates of thrombocytopenia/coagulation disorders and bleeding.

• Summary

• This cohort study, which was conducted among 18-65-year-olds, found that increased rates of venous thromboembolism were observed within 28 days of ChAdOx1-S vaccination in Denmark and Norway, corresponding to 11 excess events per 100 000 vaccinations, including 2.5 excess cerebral venous thrombosis events per 100 000 vaccinations. Furthermore, the vaccinated group had slightly higher rates of thrombocytopenia, coagulation disorders, and bleeding. As a result, the absolute risks described in this study are small in light of the proven benefits of covid-19 vaccination and the globally high incidence of SARS-CoV-2 infection.