Researchers at Oxford University have found that the risk of a blood clot is rare in general, but it is higher for people infected with Covid-19 than for people who have received the three vaccines authorized in the United Kingdom, made by AstraZeneca. , Modern and Pfizer.
The study, which was published Thursday on the Oxford website before being published in a scientific journal, says the risk of cerebral venous thrombosis or CVD (also known as cerebral venous thrombosis or CVST) after Covid-19 infection is about “100 times larger than normal and several times higher than it is after vaccination or after the flu,” in all age groups.
“Covid-19 significantly increases the risk of CVD, which adds to the list of blood clotting problems that cause this infection,” said Paul Harrison, a professor of psychiatry and head of the University’s translational neurobiology group. of Oxford.
Oxford University, which developed the AstraZeneca vaccine, said the research comes from an independent part of the university and is not connected to the vaccine team. The data used have been obtained from external sources, specifically from the European Medicines Agency.
Compared to the risk of clots in all three vaccines, the risk of infection is “8 to 10 times higher and, compared to baseline, about 100 times higher for infection,” Oxford said in a press release. According to research, compared to mRNA vaccines (Pfizer and Moderna), the risk of CVD due to Covid-19 infection is approximately 10 times higher. Compared to AstraZeneca, the risk of a CVT of 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 of Covid-19, 489,871 vaccinated cases and 172,724 cases of influenza, the study found that 30% of TVC cases occurred in the younger age group. 30 years, the most at risk of blood clots.
“Taking into account the risk-to-risk balances of COVID-19 is higher than that seen with current vaccines, even for those under 30; which should be taken into account when considering the balances between the risks and benefits of vaccination, ”Harrison added.
Dr Maxime Taquet, of the Translational Neurobiology Group in Oxford and co-author of the study, warned that data was still accumulating. Researchers also have yet to determine whether Covid-19 and vaccines lead to TVC in the same way, he said.
Experts noted that TVC is so rare that there is limited data even before the pandemic, and that data and data sources around Covid-19 vaccines are inconsistent and limited.
“Overall, the main finding is that these TVC events are very rare (some in every million people involved) in Covid-19 patients and in people who had one of the vaccines, but they were much rarer in people who they had a vaccine. that in people who had Covid-19, “said Kevin McConway, professor emeritus of applied statistics at Open University, in a comment at the Science Media Center in the UK. “Researchers do not claim that vaccines do not increase the risk at all compared to the risk in people who have not been vaccinated and have not had Covid-19, but say that the risk of CVD in people who have had Covid- 19 is about 100 times the risk in the general population. “
Some background: European and British drug regulators last week announced a “possible link” between the AstraZeneca vaccine and rare cases of blood clots, and the UK announced it would offer people under 30 an alternative vaccine. Other countries have followed suit and only offer older people or are like Denmark and Norway, leaving the vaccine in complete danger. While advising the public to watch for clot signs, regulators said the benefits of the shot are still worth the risk. The AstraZeneca vaccine is not authorized for use in the United States.
Six reports of similar clotting events following vaccination with the Johnson & Johnson single-dose vaccine prompted the U.S. Centers for Disease Control and Prevention and the U.S. Food and Drug Administration to recommend a break in the administration of the vaccine to allow for further investigation.
Six women between the ages of 18 and 48 had developed cerebral venous thrombosis, a clot in the area of the brain that collects and drains oxygen-depleted blood. Anticoagulants, the typical treatment for clots, should not be used in these 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 vaccine launch, has also stopped using the shot. The European Medicines Agency is expected to announce a decision on the administration of the Johnson & Johnson vaccine next week.
The WHO said on Thursday that “for now the risk of getting 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, considering it “effective in reducing COVID-19 hospitalization and preventing deaths.”