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UK study on blood clots, vaccines and Covid-19 has some “procedural gaps”

A staff member of the National Health Service is preparing for the Oxford / AstraZeneca Covid-19 vaccine in London on 21 March.
A staff member of the National Health Service is preparing for the Oxford / AstraZeneca Covid-19 vaccine in London on 21 March. Dinendra Haria / SOPA Images / LightRocket / Getty Images

Researchers at Oxford University found that the risk of a rare type of blood clot was generally lower, but higher for people infected with Covid-1

9 than among people who received the three vaccines approved in the UK – those made by AstraZeneca, Moderna and Pfizer.

The study, published in a pre-press release Thursday on the Oxford website before being published in a scientific journal, says the risk of cerebral venous thrombosis or CVT – also known as cerebral venous sinus thrombosis or CVST – after Covid-19 infection is about “100 times greater than normal and several times higher than after vaccination or after influenza ‘, in all age groups.

“Covid-19 markedly increases the risk of CVT, adding to the list of blood clotting problems caused by this infection,” said Paul Harrison, a 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 study was part of a university and not related to the vaccine team. The data used were obtained from external sources, in particular from the European Medicines Agency.

Compared to the risk of clots from the three vaccines, the risk of infection is “between 8-10 times higher and, compared to baseline, approximately 100 times higher for infection,” Oxford said in a news release. According to the study, compared to the mRNA vaccines – Pfizer and Moderna – the risk of CVT from infection with Covid-19 is about 10 times higher. Compared to AstraZeneca, the risk of CVD from Covid-19 is about eight times higher. The Johnson & Johnson Covid-19 vaccine was not included in the analysis.

Using an electronic network of health records with over 500,000 positive cases of Covid-19, 489,871 vaccinated cases and 172,724 cases of influenza, the study found that 30% of CVD cases occurred in the under-30 age group, which is the highest -exposed to the risk of blood clots.

‘Given the risk-risk balance of COVID-19, is higher than that seen with current vaccines, even for those under 30 years of age; something to consider when balancing the risks and benefits of vaccination, ”added Harrison.

Dr Maxim Take of the Oxford Group on Translational Neurobiology and co-author of the study warned that the data was still accumulating. Researchers have yet to determine whether Covid-19 and vaccines cause CVT in the same way, she said.

Experts note that CVD is so rare, there is limited data even before the pandemic, and data and data sources around Covid-19 vaccines are inconsistent and limited.

“Overall, the main finding is that these CVT events are very rare – a few in every million people involved – in patients with Covid-19 and in people who have had one of the vaccines – but they are much less common in people who have have had a vaccine than people who have had Covid-19, “said Kevin McConway, an honorary professor of applied statistics at the Open University, in a comment to the Science Media Center in the UK. “Researchers do not say that vaccines do not increase the risk at all compared to the risk in people who have not been vaccinated and also have not had Covid-19 – but they say that the risk of CVD in people who have had Covid-19 is about 100 times more than the risk among 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, with the UK announcing it would offer people under the age of 30 an alternative vaccine. Other countries have followed suit, either offering only to people over a certain age, or like Denmark and Norway, rejecting the vaccine altogether. While advising the public to watch out for signs of clots, regulators said the benefits of the shot were still worth the risk. AstraZeneca is not approved for use in the United States.

Six reports of similar clotting events following vaccination with the Johnson & Johnson single-dose vaccine prompted the US Centers for Disease Control and Prevention and the US Food and Drug Administration to recommend a pause in the vaccine to allow for further investigation.

Six women between the ages of 18 and 48 have 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 clots, should not be used in such cases. The six reported cases are among more than 6.8 million doses of Johnson & Johnson vaccine administered in the United States.

The EU, which relies heavily on the J&J vaccine to bolster its backlog of vaccinations, has also halted use. The European Medicines Agency is expected to announce a decision on the Johnson & Johnson vaccine next week.

The WHO said Thursday that “so far, the risk of 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 for the AstraZeneca vaccine for all eligible adults, calling it “effective in reducing COVID-19 hospitalization and preventing death.”

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