'No reason for widespread concern' over vaccines and rare clots, say MRC and Sisonke researchers

Risk of developing blood clots after a Covid-19 vaccination is much lower than the risk of clotting after being infected with Covid-19, a University of Oxford study found

Claire Keeton Senior features writer
SA Medical Research president Glenda Gray, left, and UCT professor Linda-Gail Bekker, the two co-principal investigators of the Sisonke implementation study, carrying the first dose of vaccine through Khayelitsha Hospital.
SA Medical Research president Glenda Gray, left, and UCT professor Linda-Gail Bekker, the two co-principal investigators of the Sisonke implementation study, carrying the first dose of vaccine through Khayelitsha Hospital.
Image: File photo

The risk of developing extremely rare blood clots after a Covid-19 vaccination — whether the Johnson & Johnson, Oxford-AstraZeneca or the mRNA vaccines of Pfizer and Moderna — is much lower than the risk of clotting after being infected with Covid-19, a new study by the University of Oxford has found.

The Sisonke study being used to vaccinate health-care workers in SA with the J&J shot was temporarily paused on Tuesday night. This came after a recommended pause in its rollout by US regulatory authorities after the detection of a rare and unusual clotting syndrome among six out of 6.8 million Americans who got the vaccine.

On Friday, the SA Medical Research Council and Sisonke scientists released a statement on the pause decision and concerns about blood clots.

“Sisonke investigators are working with SA Health Products Regulatory Authority and haematology experts to review study procedures, the consent process and management of side effects with a view to restarting vaccination,” they said.

The clotting disorder which affects the brain (known as cerebral venous thrombosis, or CVT) is about 100 times greater among people who get Covid-19 than normal, the Oxford scientists showed.

The Oxford scientists, led by Prof Paul Harrison and Dr Maxime Taquet, compared the rare clotting risk among more than 480,000 people who got a Covid-19 vaccine to more than half a million Covid-19 patients. Their study, not yet peer reviewed, found:

  • about 39 Covid-19 patients in a million got CVT;
  • about four people in a million got CVT after getting the Pfizer or Moderna mRNA vaccines; and
  • about five people in a million reported CVT after the first dose of the AstraZeneca-Oxford vaccine.

The SA Medical Research Council made the following points on Friday:

ON SAFETY

Safety monitoring is more thorough in a study than in a national rollout. After vaccination, participants are followed up and they can call the Sisonke Desk toll-free number 24/7 to report side effects or adverse events.

An independent safety physician reviews cases which have been flagged as a serious concern. Safety reports are forwarded to Sahpra.

J&J VAX SIDE EFFECTS

Only 134 people (one in 2,000) visited an emergency room or hospital for further evaluation. “One person experienced a severe allergic reaction that met the international diagnostic criteria for anaphylaxis but has since made a swift and complete recovery.”

About 81% had “reactogenicity”, showing their body was reacting to the vaccine, typically a day or two after their shot. They were mostly minor, local or systemic reactions.

VITT

VITT — which stands for vaccine-induced thrombosis (clots) and thrombocytopenia (low platelets) syndrome — was first identified in the UK and Europe after millions of AstraZeneca-Oxford vaccinations.

“People affected by it have presented with blood clots in large veins draining the brain (cerebral venous sinus thrombosis) and abdomen (splanchnic vein thrombosis) and not in the places where clots usually form like the leg, or chest.

“Cases have been characterised by low levels of platelets — a component of your bloodstream that assists with clotting and the prevention of bleeding.

“Cases do not present immediately but rather between 4 to 20 days after vaccination.”

SYMPTOMS

“Symptoms of a cerebral venous sinus thrombosis (CVST) include a severe unrelenting headache, often associated with blurred vision, difficulty speaking, weakness on one side of the body and vomiting.

Around five cases of (rare brain clotting) per million unrelated to vaccination occur in the general population, often in younger women, associated with contraception and smoking.

“About five cases of CVST per million population, unrelated to vaccination occur in the general population, often in younger women, associated with contraception and smoking.

“Splanchnic vein thrombosis presents with persistent abdominal pain and vomiting and is exceedingly rare in the general population.

“Some people have also reported bleeding and noted small blood spots about the site of their injection.”

VITT COMPLICATIONS

“The reason it is important to recognise this extremely rare side effect is because management differs from the usual way in which clots are treated.”

Rapid and effective treatment can “mitigate these serious complications”.

The number of cases is too low to know whether women are more affected than men, though it has until now mostly affected women.

ADVICE TO VACCINE RECIPIENTS

“There is no reason for widespread concern. This is an extremely rare complication affecting between one and 4 per million people who are vaccinated.”

Seek care urgently, say you were vaccinated and ask your doctor to get in touch with the Sisonke team.

“The headache from cerebral venous sinus thrombosis due to VITT has only been reported four days or more after vaccination (most commonly nine days) and is extremely severe and unrelenting.”

ADVICE TO DOCTORS & NURSES

“We ask that all doctors and nurses, especially those who work as general practitioners or in emergency rooms, establish a history of vaccination when seeing acutely unwell patients.

“VITT can be rapidly and easily detected using a simple full blood count to look at platelet levels. We urge all doctors and nurses (suspecting VITT) ... to make immediate contact with the Sisonke Desk ... Heparin and platelet infusions should be avoided.”

RISK VS BENEFITS

Covid-19 has killed more than three million people globally and left millions with long-term effects — and vaccines are one of the most effective ways to end the pandemic.

“We welcome the extension of registration on EVDS to phase 2 recipients today.

“Extremely rare side effects are unavoidable when tens of millions of vaccines are provided, but systems are in place to detect these early, assess risk factors and guide treatment.

“The risk of clots from Covid-19 itself is extremely high.

“Higher rates of blood clots are seen with medications we use daily like contraception, and with other conditions such as obesity, diabetes and cardiovascular disease as well as smoking compared with VITT.”

Countries which have paused rollouts, like the US, have already vaccinated more than a third of their population.

The Sisonke study is a collaboration between the department of health, SA Medical Research Council, Desmond Tutu Health Foundation, CAPRISA, Janssen and Johnson & Johnson.

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