Blood Clot Risk Higher From COVID-19 Than After Vaccination: Study
The researchers looked into rates of thromboembolic events – blood clots – and thrombocytopenia.
The study which was conducted by a team of researchers at the University of Oxford was published in the British Medical Journal (BMJ) on Friday.
The researchers analysed the data from over 29 million people who had received their first dose of either the Oxford-AstraZeneca vaccine or the Pfizer-BioNTech vaccine.
They used data collected from across England between 1 December, 2020 and 24 April, 2021.
What the Researchers Looked At
The researchers compared rates of adverse events after vaccination with rates of the same events after a positive SARS-CoV-2 test result.
They looked into rates of thromboembolic events – blood clots – and thrombocytopenia, a condition with low platelet counts following COVID-19 vaccination.
In addition to thrombocytopenia and blood clots, the researchers also looked at certain other risks, including CVST (blood clots in the brain) and ischaemic stroke (a blood clot or blockage that cuts off the blood supply to the brain), according to The Guardian.
What They Found
The researchers concluded that for both these vaccines, for short time intervals after the first does, there are increased risks of some blood-related adverse events leading to hospitalisation or death.
However, they also said that the risk of these adverse events is substantially higher and for a longer period of time, following infection from COVID-19.
The data showed that 107 out of 10 million people would be hospitalised or die from low platelet counts within 28 days of receiving a first dose of the AstraZeneca vaccine. This number rose to 934 people per 10 million following a positive test for coronavirus.
For ischaemic strokes, there would be an estimated 1,699 extra cases for every 10 million people after infection, while there would be only 143 extra cases after the first Pfizer jab.
“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," Lead author Julia Hippisley-Cox, professor of clinical epidemiology and general practice at the University of Oxford, was quoted as saying by The Guardian.
Fears over blood clots have led to the restricted use of the Oxford-AstraZeneca vaccine in a number of countries.
(With inputs from The Guardian.)
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