Covid-19 vaccine: Blood-clot risk rarer than a double lightning strike

18 April 2021 - 00:00 By Claire Keeton and Tanya Farber
A new study shows people have an eight times greater risk of developing severe cerebral blood clots from Covid-19 than from the Oxford/AstraZeneca vaccine.
A new study shows people have an eight times greater risk of developing severe cerebral blood clots from Covid-19 than from the Oxford/AstraZeneca vaccine.
Image: REUTERS/Yves Herman

You have a greater chance of being struck by lightning - twice - than getting a blood clot from a Covid-19 vaccine.

"To stop the vaccinations and put our health-care workers at risk is unethical and not the correct thing to do," said Wits professor Barry Jacobson, president of the SA Society of Thrombosis and Hemostatis, after the Johnson & Johnson vaccine rollout to health workers was suspended on Tuesday.

The move followed a pause in administration of the J&J vaccine by the US Food and Drug Administration (FDA), to give it time to investigate the risk of very rare (one to four people in a million) and unusual blood-clotting disorders that could be linked to the jabs.

None of the 292,623 health workers vaccinated in SA has developed severe clotting.

Jacobson said: "I have treated doctors who have died from Covid-induced thrombosis ... there is no science or ethics to this suspension. People should fight to continue with the vaccinations."

A new study by Oxford University scientists shows people have an eight times greater risk of developing severe cerebral blood clots from Covid-19 than from the Oxford/AstraZeneca vaccine.

About 40 people in a million developed cerebral blood clots in the two weeks after a Covid-19 infection and about eight died, the researchers found. In comparison, about four to five people in a million who got the AstraZeneca vaccine were at risk of clots.

About 500,000 cases of Covid-19 in the US were analysed for the latest study, which has yet to be peer reviewed.

SA's decision to suspend its vaccinations followed the FDA pause sparked by blood clots in six out of 6.8-million Americans who had the J&J vaccine, one of whom died.

The SA Medical Research Council said: "Some countries, like France and Poland, have weighed the risks and chosen to continue to provide the J&J vaccine while this rare side-effect is considered.

"The US has suspended use of the J&J vaccine for now but in a context where 37% of their population have already received one vaccination, and where alternatives are readily available."

Dr Keith Cloete, head of health in the Western Cape, said the J&J vaccine was made available in SA under trial conditions. "When the FDA announces a pause, our science institutions and ethics committees are virtually bound by that decision."

Professor Linda-Gail Bekker, co-principal investigator of the Sisonke implementation study, which has been delivering the J&J vaccines, said: "We had a very good meeting with Sahpra [ SA Health Products Regulatory Authority] and there is ... urgency on this."


Once the FDA reached a decision, Sahpra could act. "We must wait and see," Bekker said, adding that the Sisonke study team had 200,000 doses in hand and was ready to resume vaccinations as soon as it could.

"We were planning to be finished by the first week of May but this could eat into May," Bekker said of their goal to protect half a million health workers.

Co-principal investigator professor Glenda Gray said they respected the Sahpra process given that safety was paramount.

"We have spoken to haematologists and immunologists who say the risk of Covid-19 outweighs the very rare clotting events. We know Covid-19 induces thrombotic events and the vaccine in some way mimics infection [to boost immunity]," she said.

Sisonke has updated information and consent forms for study participants. Bekker said the rare clotting disorder seemed to develop within four to 20 days of vaccinations and people should watch out for blinding, unremitting headaches or abdominal pain, new-onset seizures, loss of vision or cloudy vision, new leg pain or shortness of breath.

"People should see a doctor and get hold of our safety desk [if they develop these symptoms]. They should avoid heparin [a blood thinner] until they know about their diagnosis."

The condition is treatable and doctors have treated its cousin, "heparin-induced thrombosis", before, she said.

Professor Ken Boffard, trauma director at Milpark Hospital, said out of 32-million people in the UK who had received the AstraZeneca jab, 16 had developed clots.

"Everybody's worried the hell out of the AstraZeneca vaccine, which has the world's most comprehensively documented safety trial in history," he said. "[But] 16 out of 32 million? Get real, guys."

AstraZeneca vaccinations in several European countries were briefly paused last month to investigate rare blood-clotting disorders, and later resumed.

Wits vaccinology professor Shabir Madhi said a side-effect of one in a million was "almost impossible to see in a trial of 30,000-35,000, only half of whom get the actual vaccine."

- Additional reporting by Paul Ash


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