Genetic Predisposition Linked to Rare Blood Clots Following AstraZeneca and Johnson & Johnson COVID Vaccines
A new study published in The New England Journal of Medicine sheds light on the cause of vaccine-induced immune thrombotic thrombocytopenia (VITT), a rare but potentially fatal condition linked to adenovirus-based COVID-19 vaccines from AstraZeneca and Johnson & Johnson. Researchers have identified a genetic component that, combined with a chance mutation, appears to trigger the dangerous immune response.
Months after the initial rollout of COVID-19 vaccines in 2021, concerns arose regarding an exceedingly rare but deadly side effect associated with the AstraZeneca and Johnson & Johnson shots. These vaccines were linked to dangerous blood clotting, prompting pauses in their use and eventual removal from the market. Despite these measures, the underlying cause remained a mystery—until now.
Unraveling the Mystery of VITT
The condition, initially dubbed vaccine-induced immune thrombotic thrombocytopenia (VITT) by a team led by Andreas Greinacher, a blood expert at the University of Greifswald in Germany, initially baffled scientists. Early theories centered on a reaction to the adenoviruses used in both vaccines—engineered to stimulate an immune response to the coronavirus but considered harmless. Researchers observed that patients with VITT exhibited antibodies binding to a chemical signal released by platelets, suggesting the immune system was mistakenly attacking blood components. Another possibility focused on a reaction to the spike protein present in the immunization.
The new research confirms the first theory: VITT is a response to the adenovirus itself, but with a crucial caveat—a genetic predisposition. Scientists examined antibodies in stored blood samples from 21 VITT patients and discovered a subset capable of binding to both a portion of the adenovirus and to PF4, a molecule influencing blood clotting. Importantly, antibodies from individuals who received the vaccine without developing VITT did not exhibit this cross-reactivity.
The Role of Genetics and Mutation
Further investigation revealed a link between the immune cells responsible for VITT and two specific DNA variants. A broader survey of 100 VITT patients confirmed that all possessed immune cells with one of these genetic types, indicating a strong risk factor. However, the study also demonstrated that this genetic background alone wasn’t sufficient to cause VITT.
The dangerous antibodies were produced only after the immune cells experienced an additional, small genetic change—a mutation that prompted the production of these cross-reactive molecules. This finding echoes previous research suggesting genetic predispositions can explain adverse events following vaccination, such as a link between a swine-flu vaccine and narcolepsy in Europe. However, this new study provides the first concrete evidence of how a specific DNA variant can lead to self-sabotaging antibodies after vaccination.
“The paper is a landmark finding because of how elegantly it explains the way a specific genetic trait, combined with a particular chance mutation in certain cells, creates VITT,” stated a biomedical engineer at the University of Sydney. The involvement of multiple genetic changes also explains the rarity of the immune reaction, he added.
Implications for Vaccine Design and Public Trust
While this discovery is unlikely to immediately impact individual vaccination choices—most recipients won’t know their genetic predisposition—it will significantly guide future vaccine development. Experts believe this work will advance the field of precision vaccinology, where vaccines are tailored to individual traits.
“Instead of abandoning an entire vaccine platform because of a rare problem, we can engineer around the specific issue, and that’s the power of this kind of science,” explained a researcher at the Precision Vaccines Program at Boston Children’s Hospital. Designing adenovirus-based vaccines without the protein region triggering the dangerous antibodies could make them safer.
The findings also bolster public trust in vaccines by demonstrating a commitment to understanding and addressing rare adverse events. According to Greinacher, adenovirus-based vaccines remain vital, particularly for developing nations and for rapid response during future pandemics.
Ongoing Research and Remaining Questions
Despite this breakthrough, the story isn’t fully closed. A separate study suggests a biophysical mechanism—independent of the immune reaction identified in VITT—may cause a component of the AstraZeneca vaccine to directly aggregate platelets. Furthermore, the underlying reasons why infections themselves sometimes lead to dangerous blood clotting remain unclear.
An immunologist at King’s College London noted that the new study, by revealing how similarities between a virus particle and a clotting protein can confuse the immune system, could offer insights into this broader question. Ultimately, understanding why viruses provoke immune overreactions may help limit damaging complications from illness itself.
