After AstraZeneca, Johnson & Johnson Covid-19 vaccine has blood clot concerns

Although having shown a similar side effect, the AstraZeneca and Johnson & Johnson vaccines differ hugely

Within a few weeks after a number of nations temporarily stopped administering doses of the AstraZeneca Covid-19 vaccine over reports of blood clots, the United States on Tuesday paused the production of the Johnson & Johnson vaccine for the same reason.

While one person has died, another has been hospitalised and is in a critical state. Over 6.8 million people in the United States have already received the vaccine.

Experts have yet to determine to what extent, if any, the vaccine is responsible for the clots. But the investigation follows actions by European regulators who concluded that a vaccine made by AstraZeneca may also be the cause of a similar, extremely rare clotting disorder.

Read | Johnson & Johnson coronavirus vaccine and blood clots: A risk, if it exists, is tiny

Several countries in Europe last week restricted use of the AstraZeneca-Oxford vaccine to older adults because rare cases of the blood disorder were occurring in younger people. The AstraZeneca vaccine has not been authorised in the United States.

The Johnson & Johnson vaccine issue began when six women in the United States who received the Johnson & Johnson vaccine developed a rare disorder involving blood clots within about two weeks of vaccination. In the condition, called cerebral venous sinus thrombosis, clots form in veins that drain blood from the brain. The results are “stroke-like,” Dr Anne Schuchat of the CDC said.

Researchers studying a very similar disorder in AstraZeneca recipients in Europe say it appears to be caused by an intense reaction to the vaccine by the immune system, which generates antibodies that activate platelets, a blood component that helps form normal clots to repair wounds. In addition to clots, abnormal bleeding occurs. European researchers have called the disorder identified there “vaccine-induced immune thrombotic thrombocytopenia.”

In the United States, 300,000 to 600,000 people a year develop blood clots in their lungs or in leg veins or other parts of the body, according to the CDC.

Based on that data, about 1,000 to 2,000 blood clots occur in the US population every day. With several million people a day now getting vaccinated, some of those clots will occur in those receiving the shots just by coincidence, unrelated to the vaccine.

In Britain, regulators have said, roughly one in 1,000 people are affected by a blood clot in a vein every year.

But the clotting disorder of concern in the vaccine recipients is much rarer and different from typical blood clots. In addition to clotting in the brain — called cerebral venous sinus thrombosis, or CVST for short — the patients all had a notably low level of platelets, which left them prone to abnormal bleeding.

Also Read | Five things to know about the AstraZeneca/Oxford Covid-19 vaccine

While both vaccines appear to show similar a similar side effect, this is where their similarities end.

The AstraZeneca vaccine, costing around $3.40 has been approved in several nations around the world. The significantly costlier Johnson & Johnson vaccine has been approved only by the US, European Union, South Africa and the World Health Organization.

More importantly, AstraZeneca's vaccine is a two-dose vaccine, while the Johnson & Johnson vaccine is one of the few single-dose Covid-19 shots in the world.

(With agency inputs)