Risk of blood clot after Covid infection is eight times higher than after AstraZeneca vaccine

The risk of developing a blood clot after a Covid-19 infection is eight times higher than after a dose of the AstraZeneca vaccine, a study by Oxford University has revealed.

Cerebral venous thrombosis (CVT), in which blood clots in the veins that run from the brain, occurred in 39 in a million coronavirus patients, compared to only five in a million people given the AstraZeneca jab.

The study consisted of over 500,000 Covid-19 patients, wherein risk of thrombosis (or blood clotting) was reported to be around 100 times higher after infection.

Study co-author Professor Paul Harrison said: “There is no doubt that contracting Covid-19 is a much greater risk of this than any of the vaccines.”

The results come amid global fears about the Oxford vaccine’s rare side-effect, with more than a dozen countries suspending its use, Denmark halting its rollout and Malawi having to bin 16,000 doses due to vaccine hesitancy.

The technology of harnessing an adenovirus, used to create the AstraZeneca and Johnson & Johnson vaccine has been linked to a slightly increased risk of blood clots.

Marco Cavaleri, chairman of the vaccine evaluation team at the European Medicines Agency (EMA) told newspaper Il Messaggero that brain blood clots have an “association with the vaccine,” but gave no evidence to support his claims.

With only 100 of the 21 million people vaccinated with their first dose of AstraZeneca forming these rare blood clots, the risk has been said to be lower than that of the widely used and accepted combined contraceptive pill.

The comparison has been used to show the limited risk from the vaccine, with the pill carrying a thrombosis risk of four in 10,000, as opposed to the vaccine of which the risk is four in a million.

Dr Sarah Hardman, a director at the Faculty of Sexual Health and Reproductive Healthcare Royal College of Obstetricians and Gynaecologists, commented: “People are at increased risk of thrombosis whenever they use combined hormonal contraception. Many chose to accept that risk to get the benefits.

“A very few cases of a rare specific type of thrombosis have been reported after the AstraZeneca Covid-19 vaccine. We do not know for certain that these were caused by the vaccine.

“They are rare cases, and we do not know being on combined hormonal contraception makes any difference at all to the risk of them happening.”

In March, out of the 79 reports the UK’s Medicines and Healthcare products Regulatory Agency (MHRA) received regarding formation of blood clots, 51 of the cases were found in women as opposed to 28 in men.  

However, the MHRA pointed out that more women have received the AstraZeneca than men, and many medical experts have come forward to insist there is no link between level of risk and gender.

Sir Munir Pirmohamed, chair of the UK’s Commission on Human Medicines, said that the incidence rate of rare blood clots showed “no difference” between men and women.  

Whilst the death rate from blood clots linked to the AstraZeneca vaccine is statistically low, the first death occurred in Australia yesterday.

But, the mother of Neil Astles, the 59-year-old man who died from a rare blood clot after receiving his first AstraZeneca jab dose on Easter Sunday has urged the public to continue with the vaccine rollout.

Dr Alison Astles told the Telegraph: “We trust the process, we trust the regulator, and despite what has happened to our family, we don’t want people to be scared off. That’s the message we want to get across.”

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