Covid — not vaccination — presents biggest blood clot risk: study

On Tuesday, January 12, 2021, a health care worker looks after a Covid 19 patient in the intensive care unit of the Robert Bosch Hospital in Stuttgart.

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A new study has shown that the risk of rare blood clotting is significantly higher from being infected with Covid-19 than from being vaccinated against the virus.

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

The scientists looked at the frequency of thromboembolic events – blood clots – and thrombocytopenia, a condition with low platelet counts. Rare blood clotting with low platelet counts has been linked to the Oxford-AstraZeneca Covid-19 vaccination.

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

The researchers found that the risk of these side effects after a Covid-19 infection was “significantly higher” than after receiving the Oxford-AstraZeneca or Pfizer-BioNTech vaccine.

The data

In the eight to 28 days after a first dose of the Oxford-AstraZeneca vaccine, researchers found an increased risk of rare blood clotting events and low platelet counts. At the same time after a first dose of the Pfizer BioNTech vaccine, the study found that the risk of blood clots and stroke was increased due to reduced blood flow to the brain (ischemic stroke).

However, these risks were significantly lower than the risks of a Covid 19 infection.

Researchers estimated that 107 out of 10 million people would be hospitalized or die of low platelet counts within 28 days of receiving their first dose of the Oxford-AstraZeneca vaccine. In contrast, that number rose to 934 people per 10 million after testing positive for Covid-19.

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

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

Even after being infected with the coronavirus, the risks remained higher for longer than after the vaccination, according to the study.

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

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

Vaccine studies are “unlikely” to discover very rare side effects

All of the Covid-19 vaccines currently in use in the US and UK have been tested in randomized clinical trials that are likely not large enough to detect very rare side effects, researchers found on Friday.

When rare events are uncovered, regulators conduct a risk-benefit analysis to weigh the side effects against the benefits of vaccination, the study authors added.

The UK Joint Vaccination and Immunization Committee has stated time and again that for the vast majority of people, the benefits of the Oxford-AstraZeneca vaccine continue to outweigh the risks.

Several health authorities, including the WHO, the European Medicines Agency and the International Society on Thrombosis and Hemostasis, also agree that the benefits of giving the vaccine outweigh the risks.

“People should be aware of the increased risks after a Covid-19 vaccination and immediately consult a doctor if symptoms occur, but also be aware that the risks of infection with SARS-CoV-2 are significantly higher and over longer periods of time Julia Hippisley-Cox, Professor of Clinical Epidemiology and General Practice at Oxford University and lead author of the article, said in a press release.

“This enormous study has shown that there is a very low risk of clotting and other blood diseases after the first Covid-19 vaccination. Although the risk of these consequences after a SARS-CoV-2 infection is very high, it is indeed serious, “says Aziz Sheikh. , Professor of Research and Development in Primary Care at the University of Edinburgh and co-author of the article, added.

Symptoms to look out for include new, severe headaches that aren’t relieved by common pain relievers, headaches that worsen when you lie down or stoop, unexplained bruising or bleeding, shortness of breath and leg swelling, according to the UK government.

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