Researchers at the University of Oxford have found that the risk of a rare type of blood clot is generally low, but higher in people infected with Covid-19 than in people who have received the three vaccines authorized in the UK. Uni – those manufactured by AstraZeneca. , Moderna and Pfizer.
The study, made available for pre-print Thursday on the Oxford website ahead of publication in a scientific journal, indicates the risk of cerebral venous thrombosis or CVT – also known as cerebral venous sinus thrombosis or CVST – after infection with Covid-19 is about “100 times higher than normal and several times higher than after vaccination or after influenza”, in all age groups.
“Covid-19 dramatically increases the risk of CVT, adding to the list of blood clotting problems this infection causes,” said Paul Harrison, professor of psychiatry and head of the Translational Neurobiology group at the University of Oxford.
The University of Oxford, which developed the AstraZeneca vaccine, said the research came from a separate part of the university and was unrelated to the vaccination team. The data used was obtained from external sources, in particular the European Medicines Agency.
Compared to the risk of clots from the three vaccines, the risk of infection is “between 8 to 10 times higher and compared to baseline, about 100 times higher for infection,” Oxford said in a statement. Press. According to research, compared to mRNA vaccines – Pfizer and Moderna – the CVT risk of Covid-19 infection is about 10 times higher. Compared to AstraZeneca, the risk of CVT from Covid-19 is approximately eight times higher. The Johnson & Johnson Covid-19 vaccine was not included in the analysis.
Using a network of electronic health records of more than 500,000 positive cases for Covid-19, 489,871 vaccinated cases and 172,724 influenza cases, the study found that 30% of CVT cases occurred in group d age under 30, the most at risk of blood clots.
“Considering that the balance between the risks and the risk of COVID-19 is higher than what we see with current vaccines, even for those under 30; something that should be taken into account when considering the balance between the risks and benefits of vaccination, ”added Harrison.
Dr Maxime Taquet of the Oxford Translational Neurobiology group and a co-author of the study warned that the data was still accumulating. Researchers also need to determine whether Covid-19 and vaccines lead to CVT in the same way, she said.
Experts noted that CVT is so rare that data is limited, even before the pandemic, and that data and data sources for Covid-19 vaccines are inconsistent and limited.
“Overall, the main finding is that these CVT events are very rare – a few out of a million people involved – in Covid-19 patients and in people who received one of the vaccines – but they were many more. rare in vaccinated people. than in people who had Covid-19, ”said Kevin McConway, professor emeritus of applied statistics at the Open University, in a commentary to the Science Media Center in the UK. “Researchers are not claiming that vaccines do not increase risk at all relative to risk in people who have not been vaccinated and who have not had Covid-19 either – but they say the risk of CVT in people who have had Covid-19 is about 100 times the risk in the general population. “
Some general information: European and UK drug regulators last week announced a “possible link” between the AstraZeneca vaccine and rare cases of blood clots, with the UK announcing it would offer people under 30 an alternative vaccine. Other countries have followed suit and only offer people above a certain age or are like Denmark and Norway, abandoning the vaccine entirely. While advising the public to look for signs of clots, regulators said the benefits of the shot were always worth the risk. The AstraZeneca vaccine has not been authorized in the United States.
Six reports of similar clotting events after vaccination with the Johnson & Johnson single-dose vaccine prompted the United States Centers for Disease Control and Prevention and the United States Food and Drug Administration to recommend a break in the vaccine. administration of the vaccine to allow further investigation.
Six women between the ages of 18 and 48 had developed cerebral venous sinus thrombosis, a clot in the area of the brain that collects and drains oxygen-depleted blood. Blood thinners, the typical treatment for blood clots, should not be used in such cases. The six reported cases were among more than 6.8 million doses of the Johnson & Johnson vaccine administered in the United States.
The EU, which relies heavily on the J&J vaccine to bolster its late vaccination rollout, has also suspended use of the vaccine. The European Medicines Agency is expected to announce a decision on the administration of the Johnson & Johnson vaccine next week.
The WHO said Thursday that “for now, the risk of suffering from blood clots is much higher for someone with COVID-19 than for someone who has taken the AstraZeneca vaccine.” WHO Regional Director for Europe Hans Kluge reiterated his recommendation of the AstraZeneca vaccine for all eligible adults, calling it “effective in reducing COVID-19 hospitalizations and preventing deaths.”
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