Researchers have identified an autoimmune reaction as the underlying cause of rare but deadly blood clots linked to the Johnson & Johnson and AstraZeneca Plc’s COVID-19 vaccines. This discovery is anticipated to influence the development of future vaccines, as reported by Bloomberg.
Adenovirus-based vaccines, including the J&J and AstraZeneca shots that were later withdrawn from the market, contain a component that can trigger blood clots in genetically susceptible individuals. Scientists reported this finding in a letter published Wednesday in the New England Journal of Medicine.
Researchers are currently working to identify the specific component responsible and explore the possibility of removing it through genetic engineering, according to the report. “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 discovery.
The immune reaction associated with the vaccine is considered a “new disease,” Gordon stated in an interview. “I think as haematologists and intensive care specialists become more familiar with these conditions, more cases will be described,” he added.
Out of over 18 million people who received the single-dose J&J vaccine, 60 cases of the clotting disorder were reported, resulting in nine deaths, as per data from 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.
In Australia, where the AstraZeneca vaccine has not been available since March 2023, the complication occurred in approximately 2-3 people per 100,000 vaccinated under the age of 60. The European Commission withdrew the marketing authorization for the AstraZeneca vaccine in March 2024, according to the Bloomberg report.
A spokesperson for AstraZeneca welcomed further investigation into the underlying mechanism of thrombosis with thrombocytopenia syndrome (TTS), stating, “Despite extensive investigation, we do not yet understand the mechanism that can in very rare cases be a trigger for TTS.”
Johnson & Johnson also expressed support for research that contributes to the development of safe and effective vaccines. “More data are needed to fully understand potential factors that may be associated with this rare event… to draw appropriate conclusions about the underlying pathogenesis,” the company said in an email.
Both the J&J and AstraZeneca vaccines played a significant role in early pandemic vaccine programs. An analysis revealed that the AstraZeneca vaccine saved an estimated 6.3 million lives in 2021. mRNA vaccines manufactured by the Pfizer-BioNTech partnership and Moderna Inc. were subsequently found to be more effective in protecting against COVID-19 and have been updated to combat more recent virus variants.
