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 has found that the risk of blood clotting is significantly higher as a result of Covid-19 uptake, than vaccination against the virus.
In an expert-reviewed study published in the British Medical Journal on Friday, researchers at Oxford University, the London School of Hygiene and Tropical Medicine and several other British universities and hospitals analyzed data from more than 29 million people who had received the 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.
The scientists examined rates of thromboembolic events (blood clots) and thrombocytopenia, a condition with a low platelet count. Rare blood clotting with low platelet levels has been associated with Oxford-AstraZeneca Covid-19 vaccination.
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 “substantially greater” after Covid-19 infection than after receiving the Oxford-AstraZeneca vaccine or the Pfizer-BioNTech vaccine.
The data
In the eight to 28 days following the first dose of the Oxford-AstraZeneca vaccine, the researchers identified an increased risk of rare blood clotting events and a low platelet count. In the same time period after a first dose of the Pfizer-BioNTech vaccine, the study found that it increased the risk of blood clots and strokes caused by restricted blood flow to the brain (ischemic stroke).
However, these risks were significantly lower than the risks of Covid-19 infection.
The researchers estimated that 107 out of 10 million people would be hospitalized or die from a low platelet count within 28 days after receiving a first dose of the Oxford-AstraZeneca vaccine. In contrast, that number increased to 934 people for every 10 million after a positive test for Covid-19.
At 28 days of the first dose of the Oxford-AstraZeneca vaccine, 66 people for every 10 million were hospitalized or died from blood clots in their veins, compared with 12,614 for every 10 million who had tested positive for the virus.
Meanwhile, an estimated 143 people for every 10 million were hospitalized or died of ischemic stroke during the 28 days following the first dose of the Pfizer-BioNTech vaccine, compared with 1,699 who tested positive for Covid-19. .
The risks also remained high for a longer period after contracting the coronavirus than it did after vaccination, the study concluded.
The study routinely analyzed electronic health records to assess the risk of hospital admission for blood clots and low platelet count at 28 days after infection or vaccination.
The data used in the study were collected across England between 1 December 2020 and 24 April 2021. Patients who were still in the hospital on the final date of the study were excluded. of the study.
“Unlikely” vaccine trials will detect very rare side effects
All Covid-19 vaccines currently used in the U.S. and the UK have been tested in randomized clinical trials, which are unlikely to be large enough to detect very rare adverse events, the researchers noted Friday.
When rare events are discovered, regulators perform a risk-benefit analysis to weigh the adverse effects against the benefits of receiving the vaccine, the study authors added.
The Joint Vaccination and Vaccination Committee of the United Kingdom has consistently stated that the benefits of the Oxford-AstraZeneca vaccine continue to outweigh the risks to the vast majority of people.
Several health authorities, including the WHO, the European Medicines Agency and the International Society for Thrombosis and Hemostasis, have also agreed that the benefits of vaccine administration outweigh the risks.
“People should be aware of this increased risk after vaccination against Covid-19 and should seek medical attention quickly if they show symptoms, but they should also be aware that the risks are considerably higher and for periods of time. longer if they become infected with SARS-CoV-2, ”said Julia Hippisley-Cox, a professor of clinical epidemiology and general practice at Oxford University and lead author of the paper, in a press release.
“This huge study has shown that there is a very low risk of clotting and other blood disorders after the first dose of vaccination against Covid-19. Although severe, the risk of these same results is much higher after of SARS-CoV-2 infection, ”Aziz Sheikh said. , added Professor of Primary Care Research and Development at the University of Edinburgh and co-author of the paper.
According to the UK government, symptoms to consider include a new, severe headache that does not relieve regular painkillers, a headache that gets worse lying down or crouching, unexplained bruising or bleeding, shortness of breath and swelling. of the legs.