Risk of Blood Clots Higher in COVID-19 Than AstraZeneca Vaccine

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Scientists at the University of Oxford have found that the risk of blood clots is eight times higher following COVID-19 than receiving the AstraZeneca Vaccine.

Over the past few weeks, multiple concerns regarding the COVID-19 vaccines have come forward. The most significant of which is the risk of blood clots. However, this particular concern has so far only appeared with the AstraZeneca vaccine and the Johnson & Johnson vaccine. Both of which use an adenovirus vector. As a result, several European countries have suspended the use of the AstraZeneca vaccine. Additionally, the US called for a pause of the J&J Janssen vaccine. However, a preliminary study has now found evidence of COVID-19 causing a higher risk of blood clots than the AstraZeneca vaccine. Although the study is yet to receive a peer review, its results shine new light on the importance of coronavirus vaccines.

The team of scientists at the University of Oxford aimed to investigate the incidence of cerebral venous thrombosis (CVT) following COVID-19, influenza, and receiving an mRNA or AstraZeneca vaccine. They analyzed data from more than 500,000 patients; two weeks after their COVID diagnosis. Researchers also used two control groups for comparison. Comprising of patients diagnosed with influenza, and those who had received an mRNA or AstraZeneca vaccine.

8-10 Times Greater Risk

CVT is a type of stroke that occurs due to a blood clot in the brain’s venous sinuses. Symptoms typically range from headache, blurred vision, loss of consciousness to coma. According to the results, incidence of CVT was 5 per million people in those who had received the first dose of AstraZeneca vaccine. Moreover, individuals who had received Pfizer or Moderna mRNA-based vaccines had an incidence of 4 per million. In comparison, CVT occurred in 39 per million people among the COVID positive patients. Thus, revealing the risk of the blood clots to be 10 times higher with COVID-19 compared to mRNA vaccines. Whereas compared to the AstraZeneca vaccine, the risk of blood clots with COVID-19 was 8 times higher.

We’ve reached two important conclusions. Firstly, COVID-19 markedly increases the risk of CVT, adding to the list of blood clotting problems this infection causes. Secondly, the COVID-19 risk is higher than seen with the current vaccines, even for those under 30; something that should be taken into account when considering the balances between risks and benefits for vaccination.

Professor Paul Harrison, University of Oxford

The study also reported a similar finding when investigating the incidence of portal vein thrombosis (PVT).

Despite the findings, researchers believe the results should be interpreted with caution as the data is still being gathered. However, WHO and UK’s health authorities have both spoken in favour of the AstraZeneca vaccine. Urging people to continue with their vaccinations as the benefits of the vaccine outweigh its risks.


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