Blood clot risk much higher from Covid-19 than after vaccination: Study

 The risk of blood clots is higher after infection with the SARS-CoV-2 virus than after immunisation with Pfizer and AstraZeneca Covid-19 vaccines, according to a study

The risk of developing adverse events such as blood clots is considerably higher after infection with the SARS-CoV-2 virus than after immunisation with Pfizer and AstraZeneca COVID-19 vaccines, according to a large UK study published in the British Medical Journal (BMJ) on Friday.

The team led by researchers at the University of Oxford in the UK conducted the study on thrombocytopenia — a condition with low platelet counts — and thromboembolic events or blood clots following COVID-19 vaccination with Oxford-AstraZeneca and Pfizer-BioNTech preventives. Some of these events have led to restricted use of the Oxford-AstraZeneca vaccine, known as Covishield in India, in a number of countries. The researchers compared rates of adverse events after vaccination with rates of the same events after a positive SARS-CoV-2 test result using data from over 29 million people in the UK who received the first dose of either of the two vaccines.

They concluded that with both of these vaccines, for short time intervals following the first dose, there are increased risks of some blood-related adverse events leading to hospitalisation or death. “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,” said Julia Hippisley-Cox, professor at the University of Oxford, and lead author of the research paper.