Acquired Thrombotic Thrombocytopenic Purpura: A Rare Coincidence after COVID-19 mRNA Vaccine?

We present 3 patients who developed acquired thrombotic thrombocytopenic purpura (aTTP) after receiving BNT162b2 mRNA COVID-19 vaccines. The clinical diagnoses were confirmed by the significantly reduced ADAMTS13 activities (<0.1 IU/mL) and markedly elevated auto-antibodies to ADAMTS13. We attempted to establish a causal link between the mRNA vaccine and the effectuation of aTTP. Using the ELISA methodology incubating the patients’ plasma and/or serum samples with two different commercial biotinylated recombinant COVID Spike S1 proteins, no binding to both ADAMTS13 and Covid Spike S1 protein was seen.  Although based on these assays, no cross reactivity was demonstrated between the patients’ autoantibodies to ADAMTS13 and the anti-S1 Spike protein antibody, we cannot exclude other mechanisms which may enhance autoimmunity leading to the development of aTTP.