An unmatched vaccination effort was launched to contain the coronavirus disease 2019 (COVID-19) pandemic. Despite their demonstrated efficacy and safety, adenoviral-vector vaccines have a rare but potentially fatal side effect known as vaccine-induced immune thrombotic thrombocytopenia (VITT), whose pathogenesis appears to be connected to the emergence of platelet-activating anti-platelet factor 4 (PF4) antibodies.

Although a few research have analyzed the frequency of anti-PF4 positivity in SARS-CoV-2 vaccination recipients, no studies have examined whether an antiplatelet immunological response arises and if this is linked to platelet and blood clotting activation. In order to assess immune responses that were both specific and non-specific to platelets as well as in vivo platelet activation and blood clotting activation, researchers conducted a prospective trial in healthy patients who had received the initial dose of the ChAdOx1, Ad26.COV2.S, or BNT162b2 vaccines.

People who received ChAdOx1 and, less so, Ad26.COV2.S acquired high-frequency auto- or alloantiplatelet antibodies, more platelet-derived microvesicles in the bloodstream, and soluble P-selectin linked to moderate blood clotting activation.

Specifically following ChAdOx1 and Ad26.COV2.S, the data demonstrated that an immunological reaction involving platelets is not unusual in people receiving anti-SARS-CoV-2 vaccination and that it was linked to in vivo platelet and blood clotting activation.

Reference: onlinelibrary.wiley.com/doi/10.1111/bjh.18245