The risk of developing a blood clot from catching coronavirus is eight times higher than after being given the Astrazeneca vaccine, according to a new study by the University of Oxford.
Scientists found that cerebral venous thrombosis (CVT) occurred in 39 per million coronavirus patients, compared with around 5 per million people given the Astrazeneca jab.
In the study of more than 500,000 patients in the US, the risk of developing a blood clot was reported to be around 100 times higher after contracting coronavirus than normal.
Researchers said the figures should help regulators and the public to better understand the “risk-benefit question” associated with Covid vaccines.
John Geddes, the University of Oxford, said that while blood clots did indeed appear to be an extremely rare side effect of coronavirus vaccines, it was just one of many negative side effects caused by Covid-19 infection.
“A lot of the attention has been taken away and put on the vaccine. The importance of this finding is it brings it back to the fact this is a really horrible illness that has a whole variety of effects… and I think that for us is the main finding,” he said.
Professor Sir John Bell, the university’s regius professor of medicine, added that “the best way, if you want to have a bad clotting problem, is to get Covid”.
“And if you don’t get a vaccine you’re going to get Covid, and if you get Covid you’ll have a very, very much higher risk of getting a bad clotting problem,” he told Sky News.
“So, the clotting problems of the vaccine are pretty trivial compared to the real risks of getting clotting problems if you get Covid.”
Denmark yesterday became the first country in the world to ban the use of the Astrazeneca jab altogether amid concerns over blood clot risks.
Meanwhile, US regulators earlier this week said they would suspend use of the Johnson & Johnson vaccine while they investigate similar cases of clotting.
Professor Bell suggested that other coronavirus vaccines could also have “some background level of clotting issues”.
“We don’t have clear enough data on what the risks of these strange clots actually are with the different vaccines, and that data is coming together at the moment,” he said. “I suspect there will be risks associated with the other vaccines that use the spike antigen as the target.”