Very rare thrombosis with thrombocytopenia after second AZD1222 dose: a global safety database analysis

ChAdOx1 interacts with CAR and PF4 with implications for thrombosis with thrombocytopenia syndrome

“…S10. It is notable that TTS is much less frequently observed following the second dose of ChAdOx1, suggesting that, as in HIT, αPF4 immunoglobulin G is not long lasting and that any plausible mechanism should be prominent in the first but not second dose ( 6 , 38 ). Studies are needed to confirm whether adenovirus/PF4 complexes can induce thrombosis in the presence of anti-PF4 antibodies in vivo.…”

A phase 2/3, participant-blind, observer-blind, randomised, controlled study to assess the safety and immunogenicity of SII-ChAdOx1 nCoV-19 (COVID-19 vaccine) in adults in India

“…After receiving regulatory approvals [ 9 , 10 ] millions of doses of SII-ChAdOx1 nCoV-19 as also of AZD1222 have also been distributed across many countries [12] . Very rare events of thrombosis with thrombocytopenia (TTS) and anaphylaxis have been reported from real-world use [16] , but overall data supports the continued administration of the vaccine in a two-dose schedule [17] .…”

Safety of the second dose of the ChAdOx1 nCoV‐19 vaccine in people with persistent anti–platelet factor 4 antibodies

“…The rate of thrombosis with thrombocytopenia after the second ChAdOx1 vaccination is within an estimated background range of an unvaccinated population. 1 However, safety data of the second dose of the ChAdOx1 vaccine in people with persistently positive anti–platelet factor 4 antibodies (anti‐PF4 Abs) are still lacking. Whether a second dose of the ChAdOx1 vaccine would enhance anti‐PF4 Ab production and activity leading to platelet consumption and coagulation activation remains unknown.…”