Rare but deadly blood clots tied to Johnson & Johnson and AstraZeneca Covid-19 vaccines: scientists report to journal

Rare but deadly blood clots tied to Johnson & Johnson and AstraZeneca Plc’s Covid-19 vaccines were caused by an autoimmune reaction that some people are predisposed to, researchers have found. This discovery is expected to influence the development of future vaccines, Bloomberg reported.

Adenovirus-based vaccines, like the J&J and AstraZeneca shots that were later pulled from the market, contain a component that can trigger blood clots in genetically susceptible individuals, scientists reported Wednesday in a letter to the New England Journal of Medicine. Researchers are now aiming to identify the specific component and attempt to remove it through genetic engineering, the report said.

“It’s not known how many people may be susceptible to the complication,” said Tom Gordon, head of immunology at Flinders University in South Australia, whose molecular investigation led to the finding. The immune reaction linked to the shot is “a new disease,” he stated in an interview. “I think as haematologists and intensive care specialists become more familiar with these conditions, more cases will be described," the scientists Bloomberg.

Out of more than 18 million people who received the single-dose J&J vaccine, 60 cases of the clotting disorder were reported, resulting in nine deaths, according to the Yale School of Medicine, Bloomberg reported.

A small number of clot-related deaths linked to the AstraZeneca vaccine led to its withdrawal or restriction in Denmark, Norway, and other countries in 2021. The complication occurred in about 2-3 people per 100,000 vaccinated with the AstraZeneca shot under age 60 in Australia, where it hasn’t been available since March 2023. The European Commission withdrew the marketing authorization for the vaccine in March 2024, the Bloomberg report said.

“AstraZeneca welcomes any further examination of the possible underlying mechanism of thrombosis with thrombocytopenia syndrome (TTS), given that, despite extensive investigation, we do not yet understand the mechanism that can in very rare cases be a trigger for TTS,” a spokesperson for the company said, as per the report.

J&J also expressed support for research that helps guide the development of safe and effective vaccines. “More data are needed to fully understand potential factors that may be associated with this rare event, including its potential relationship with adeno- and other viruses, to draw appropriate conclusions about the underlying pathogenesis,” the company said in an email.

Both vaccines played a crucial role in early pandemic vaccine programmes. An analysis found the AstraZeneca vaccine saved an estimated 6.3 million lives in 2021.

The mRNA vaccines made by the Pfizer Inc.-BioNTech SE partnership and Moderna Inc. were later found to be more effective at protecting against Covid and have been updated to tackle more recent virus variants.

(With Inputs from Bloomberg)