Covid – not vaccination – presents the greatest risk of blood clots: study

A health worker cares for a Covid-19 patient in the ICU ward of Robert Bosch Hospital in Stuttgart, Germany, on Tuesday, January 12, 2021.

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A new study found that the risk of rare blood clots is significantly higher due to the uptake of Covid-19, than from vaccination against the virus.

In a peer-reviewed study published in the British Medical Journal on Friday, researchers from Oxford University, the London School of Hygiene and Tropical Medicine and several other British universities and hospitals have analyzed data from more than 29 million people. who had received their first dose of either the Oxford-AstraZeneca vaccine or the Pfizer-BioNTech vaccine. The authors of the study were completely independent of the Oxford-AstraZeneca vaccine developers.

Scientists have studied the rates of thromboembolic events – blood clots – and thrombocytopenia, a disease with low platelet counts. Rare blood clotting with low platelet levels has been associated with the Oxford-AstraZeneca Covid-19 vaccine.

The paper compared rare blood clotting rates after a first dose of vaccination and after a positive Covid-19 test.

The researchers found that the risk of these adverse events was “much higher” after the Covid-19 infection than it was after receiving the Oxford-AstraZeneca or Pfizer-BioNTech vaccine.

The data

In eight to 28 days after a first dose of the Oxford-AstraZeneca vaccine, researchers have identified an increased risk of rare blood clotting events and low platelet counts. Over the same period of time after a first dose of the Pfizer-BioNTech vaccine, the study found the risk of blood clots and strokes caused by limited blood flow to the brain (ischemic stroke) increased.

However, these risks were significantly lower than the risks posed by Covid-19 infection.

Researchers have estimated that 107 out of 10 million people will be hospitalized or die from a low platelet count within 28 days of receiving a first dose of Oxford-AstraZeneca vaccine. In contrast, that number went to 934 people for 10 million after a positive test for Covid-19.

28 days after a first dose of the Oxford-AstraZeneca vaccine, 66 people out of 10 million were hospitalized or died from blood clots in their veins, compared to 12,614 out of 10 million who tested positive for the virus.

Meanwhile, an estimated 143 people out of 10 million were hospitalized or died of ischemic stroke within 28 days after a first dose of the Pfizer-BioNTech vaccine, compared to 1,699 who tested positive for Covid-19.

The risks also remained high for a longer period after the coronavirus contract than it did after vaccination, the study concluded.

The study routinely analyzed electronic health records to assess the risk of hospitalization for blood clots and low platelet counts within 28 days of infection or vaccination.

Data used in the study were collected in England between 1 December 2020 and 24 April 2021. Patients who were still in hospital at the end date of the study were excluded from the study. .

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