Risk of Vaccine-Induced Immune Thrombotic Thrombocytopenia due to Covishield

There were reports of Vaccine-induced immune thrombotic thrombocytopenia (VITT) or vaccine-induced prothrombin immune thrombocytopenia (VIPIT) following the administration of recombinant vaccine ChAdOx1 nCov which is marketed as CovishieldTM (Serum Institute of India PVT Ltd) and VaxzeviraTM (AstraZeneca). Initial studies showed that individuals under the age of 55 although some in older age groups reported VITT or VIPIT. Subsequently, numerous countries put age restrictions on the vaccine or banned it altogether. A considerable disagreement emerged between countries regarding the age at which risks outweigh benefits, ranging from age 30 in the UK, 50 in Australia, 55 in France, and 60 in Germany, Spain, and the Netherlands.

To get a clear estimate of the VITT and VIPIT which in turn is age-dependent, meta-analysis and sensitivity analysis was carried out using all the available evidence of VITT over all age groups.

The outcome of this study revealed that  VITT after the administration of ChAdOx1 nCov is rare in individuals above 65 (1 in a million) but more common in individuals below 55 (1 in 20,000 to 60,000 persons). Moreover, the risk of venous thromboembolism seemed to be high among hospitalized Covid-19 patients,  21% of non-ICU patients, and 31% of ICU patients were affected. However, the number of reported VITT cases is lower than the infections and complications of COVID-19. This information can be utilized by the policy-makers to calculate the risk-benefit ratio of the vaccine and can target the age-dependent vaccination campaigns accordingly. 

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Ref link: https://www.medrxiv.org/content/10.1101/2021.05.04.21256613v1