Abdul Mannan: Acquired Haemophilia A after Tozinameran
Abdul Mannan, Consultant Haematologist at Betsi Cadwaladr University Health Board, shared a post on LinkedIn:
“An isolated prolonged aPTT in an older patient.
No prior bleeding.
No anticoagulation.
Think carefully before you move on.
A patient presents with sudden bruising. No bleeding history. No anticoagulants.
Then the aPTT comes back prolonged. Isolated. And it doesn’t correct on mixing.
This is Acquired Haemophilia A. And it can happen after tozinameran.
Here’s what every clinician needs to know:
- AHA is rare overall, around 1.5 cases per million per year
- After tozinameran (Pfizer Comirnaty), estimated rate is 1 case per 4 million doses
- Most cases occur after dose 2, median onset around 23 days
- Skin involvement in 24 out of 27 reported cases
- Mortality sits between 8 and 20%
The proposed mechanism is molecular mimicry between the SARS-CoV-2 spike protein and FVIII sequences, triggering autoantibody production.
Diagnosis rests on three things. Isolated prolonged aPTT. Low FVIII activity. Positive Bethesda assay.
Management runs on two parallel tracks. Stop the bleeding first with FEIBA, rFVIIa, or tranexamic acid. Then target the inhibitor with steroids, cyclophosphamide if refractory, or rituximab.
One more thing. Re-exposure warning is real. Two of four re-exposed patients worsened. One died.
Extreme caution before any further tozinameran dose if vaccine-associated AHA is confirmed. Specialist haemophilia review is needed.
This does not change the overall vaccine benefit-risk balance. But pharmacovigilance matters.
Report suspected adverse reactions through the Yellow Card system.
Have you seen an unexpected prolonged aPTT in a recently vaccinated patient?”
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