The University of Aberdeen announced in October 2023 that a team of scientists has “taken an important step” towards understanding the mechanisms by which adenovirus-based vaccines, including some that were used during the COVID-19 pandemic, can cause “serious adverse reactions”. In collaboration with NHS Grampian, NHS Greater Glasgow & Clyde, and NHS Lothian, they have identified a new feature of the “ultra-rare condition” Vaccine Induced Immune Thrombocytopenia and Thrombosis (VITT).
VITT is a life-threatening condition that has been linked to the adenovirus-based vaccines for COVID-19, including Oxford/Astra Zeneca and Johnson-Johnson. A “high risk of death” from venous or arterial thrombosis or secondary haemorrhage is caused by “extreme activation of platelets and the coagulation system”.
The syndrome was first identified in March 2021 by groups in the UK, Norway, and Germany. Although thrombosis may present at any site, the majority of VITT cases presented with thrombosis in “unusual sites”. Further to thrombosis and thrombocytopenia, patients presented with “high D-dimer levels and hypofibrinogenemia”. Pathological antibodies to platelet factor 4 (PF4) were identified in early reports.
Samples in Scotland
A team, led by Professor Nicola Mutch, analysed samples from all suspected cases of VITT in Scotland. Some patients were confirmed to have the condition based on the presence of antibodies to PF4 and other clinical features, including blood clots. Professor Emeritus Henry Watson commented that the researchers identified a “unique opportunity” in the fact that Aberdeen “held all of the Scottish samples of suspected VITT”.
“This research was triggered by the recognition of the catastrophic outcomes of VITT.”
Patients with VITT had a “very high incidence” of disseminated intravascular coagulation (DIC), which can cause organ damage or uncontrolled bleeding. The team also identified an “overactivation” of the body’s natural “blood clot busting system”. This is known as fibrinolysis. When uncontrolled, fibrinolysis leads to a breakdown in the “main building block of a blood clot”, fibrinogen. Results, published in the Journal of Thrombosis and Haemostasis, can help explain the clot formation and bleeding complications that are seen in VITT patients.
Not only does this research offer insight into vaccine safety but is a “vital” contribution as a “missing piece of the jigsaw” for other aspects of medicine. Adenoviruses are used as vectors in gene therapy for cancers and haemophilia. Thus, an understanding of the mechanisms by which adenovirus-based products cause adverse reactions, facilitates better therapeutic strategies to similar conditions and informs future use in medicinal products.
Professor Mutch states that this work “helps us to understand the mechanisms underlying the clinical observations”.
“The demonstration of overt disseminated intravascular coagulation and the breakdown of the clotting protein fibrinogen in VITT had not previously been recognised but this helps explain the acute symptoms and repaid course of this extremely rare complication of vaccination with adenovirus-based vaccines.”
We look forward to exploring VITT in greater detail during the pre-Congress workshop day in Barcelona next week. You can get tickets to join us here now, or subscribe for more insights into vaccine safety.