Venous Thromboembolic Event Rates Up With ChAdOx1-S Vaccine

The rates of venous thromboembolic events, including cerebral venous thrombosis, are increased among recipients of the Oxford-AstraZeneca vaccine ChAdOx1-S, although the absolute rates are small, according to a study published online in The BMJ.

Anton Pottegård, PhD, from the University of Southern Denmark in Odense, and colleagues conducted a population-based study involving all people aged 18 to 65 years who received a first vaccination with ChAdOx1-S from Feb. 9 to March 11, 2021 (148,792 people in Denmark and 132,472 in Norway). The general populations of Denmark and Norway served as comparator controls.

The researchers found that the standardized morbidity ratio for arterial events was 0.97 (95 percent confidence interval, 0.77 to 1.20) among 281,264 people who received ChAdOx1-S. The vaccinated cohort had 59 venous thromboembolic events compared with 30 expected events based on the incidence rates in the general population, corresponding to a standardized morbidity ratio of 1.97 (95 percent confidence interval, 1.50 to 2.54) and 11 excess events per 100,000 vaccinations. The rate of cerebral venous thrombosis was higher than expected, with a standardized morbidity ratio of 20.25 (95 percent confidence interval, 8.14 to 41.73). There were 15 deaths reported in the vaccine cohort compared with 44 expected.

“Those countries that delayed their own vaccination programs at a time of high transmission rates by declining to use available Oxford-AstraZeneca vaccines should know that their decision will have contributed to an increase in the number of avoidable deaths from COVID-19,” writes the author of an accompanying editorial.

Several authors disclosed financial ties to pharmaceutical companies, including those that make vaccines against severe acute respiratory syndrome coronavirus 2.

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