PB0166 - Five cases of Acquired Haemophilia A (AHA) following COVID-19 vaccination in Australia

Background: Acquired Haemophilia A (AHA) is a rare but devastating acquired bleeding disorder, caused by autoantibodies against Factor VIII (FVIII). Up to 50% are associated with an underlying disorder including autoimmune disease, malignancy or pregnancy with the remainder considered idiopathic. There have been case reports of AHA occurring post vaccination, including following influenza and mRNA-based COVID-19 vaccination. Here we report on five cases of AHA following adenovirus-vector COVID-19 (ChAdOx1 nCoV-19) vaccination in Australia.

Aims: Report on the clinical characteristics of five patients diagnosed with AHA following ChAdOx1 COVID-19 vaccination

Methods: We collected clinical details of cases of AHA reported after COVID-19 vaccination in Australia.

Results: Five patients were identified. All were aged >70 years and presented between 19- and 35-days following ChAdOx-1 vaccination. Table 1 outlines baseline and disease characteristics and outcomes. All presented with bleeding requiring hospitalisation; two subcutaneous, one oropharyngeal, one intramuscular and one presented with subcutaneous bleeding initially and subsequently had a large retroperitoneal haemorrhage. Three required bypassing agents (BPA) to control bleeding. No underlying aetiology was found despite investigation for malignancy and autoimmune disease. Four received first-line dual immunosuppressive therapy (prednisolone with either cyclophosphamide or rituximab) and one received triple therapy (prednisolone, cyclophosphamide and rituximab). One also received intravenous immunoglobulin (IVIg). All achieved complete remission.

Conclusion(s): We report on five cases of AHA occurring following ChAdOx-1 COVID-19 vaccination. Autoimmune disorders are known to occur post vaccination, with postulated mechanisms including antigenic mimicry and non-specific activation of quiescent autoreactive T and B cells. While there was a clear temporal relationship between all five cases of AHA and the ChAdOx-1 COVID-19 vaccination, all were aged >70 years, the age group more likely to be affected by AHA. Causation cannot be definitively proven, however these cases may highlight the risk of a rare adverse event following immunisation (AEFI).