Over time, the need to revisit and refine public health concepts becomes apparent to ensure they remain accurate and relevant. This process often involves validating these definitions to enhance their precision and applicability. This approach is reflected in some of the terms in AESI lists developed by Safety Platform for Emergency vACcines (SPEAC).
Recently, Brighton Collaboration and SPEAC (funded by CEPI (Coalition for Epidemic Preparedness Innovations)) published a short communication on a study validating a *proposed* case definition for Vaccine-Induced Immune Thrombocytopenia and Thrombosis (VITT). The definition was retrospectively validated by the Case Definition Working Group and SPEAC Evaluation Lead before it was officially published.
Vaccine-induced Immune thrombocytopenia and thrombosis (VITT) is a newly recognized syndrome mediated by anti-platelet factor 4 antibodies Induced by Covid-19 adenovirus-vectored Vaccines Including ChAdOx1n CoV-19 and Ad26.COV2.S.
Key Components of the New Definition:
Thrombocytopenia:
A critical criterion for VITT is the presence of thrombocytopenia, observed in 98%-100% of VITT cases in the study. This significant reduction in platelet count is a defining feature of the condition.
Thrombosis or Thromboembolism:
A key case definition criterion is thrombosis or thromboembolism. This criterion was fulfilled in 100% of cases from the UK and Germany, 90% of cases from Australia, and 34% of cases from Taiwan. These variations underscore the importance of evaluating thrombotic events across different populations and data collection systems.
Diagnostic Levels of Certainty (LOC):
The definition enables classification into VITT levels of certainty (LOC): 1 = definite; 2 = probable; 3 = possible; 4 = unable to meet any LOC; 5 = Not a case because an alternate diagnosis explains the illness. The definition maintained reasonable sensitivity (89% to 100%) overall.
Exclusion of Alternative Diagnoses:
The definition initially required the absence of alternative diagnoses for a case to be classified as VITT. However, a revision now allows for the presence of alternative diagnoses in level 1 VITT cases, which may impact case classification in some contexts.
Read the full article at Validation of the newly proposed Brighton Collaboration case definition for vaccine-induced immune thrombocytopenia and thrombosis
