COVID increases risk of blood clotting more than vaccination: Oxford-led study

According to a UK study published in the British Medical Journal (BMJ) on Friday, the risk of experiencing adverse events such as blood clots is significantly higher following infection with the COVID-19 virus than after vaccination with Pfizer and AstraZeneca. The study looked at thrombocytopenia (low platelet counts) and thromboembolic events (blood clots) after the Covid-19 vaccination with Oxford-AstraZeneca and Pfizer-BioNTech preventives by researchers from the University of Oxford in the United Kingdom.

Research analyses data of 29 million people

Using data from almost 29 million people in the UK who received the first dose of either vaccine, the researchers compared adverse events after vaccination with rates of the same occurrences following a positive SARS-CoV-2 test result. They determined that there are higher chances of various blood-related adverse events leading to hospitalisation or death with both vaccines for brief time intervals following the first dose.

Julia Hippisley-Cox, a lecturer at the University of Oxford and the research paper's lead author, remarked, "people should be aware of these increased risks after Covid-19 vaccination and seek medical attention promptly if they develop symptoms, but also be aware that the risks are considerably higher and over longer periods of time if they become infected with SARS-CoV-2." 

According to scientists, the likelihood of these adverse outcomes is much larger and lasts much longer after infection with the coronavirus than after either vaccine. All existing coronavirus vaccines have been studied in randomised clinical trials, which are unlikely to be large enough to uncover relatively rare side events. 

With data collected from across England between December 1, 2020, and April 24, 2021, the study evaluated the short-term risks within 28 days of hospital admission with thrombocytopenia, venous thromboembolism (VTE), and artery thromboembolism (ATE). CVST (cerebral venous sinus thrombosis), ischemic stroke, myocardial infarction, and other rare arterial thrombotic events are among the different outcomes investigated.

Authors note study has limitations

Aziz Sheikh, a co-author of the paper and a professor at the University of Edinburgh, said, "this massive study has demonstrated that there is a very minimal risk of clotting and other blood issues following first-dose Covid-19 vaccination. Though dangerous, the probability of these same effects after SARS-CoV-2 infection is substantially higher." The authors noted that their study had some limitations, such as analysing only the first vaccine dosage, having a short vaccination exposure window, and the possibility of misclassifying outcomes or exposures while patients were still in the hospital. 

(Inputs from PTI)

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