The formation of complexes between PF4 and the antibody can trigger platelet activation, enhancing thrombosis risk.[9] Vaccine-induced thrombotic thrombocytopenia associated with adenoviral COVID-19 vaccines results in anti-PF4 antibodies, triggering thrombosis in patients.[14] On the other hand, a cross-sectional study by Tao et al revealed that vitamin D has a protective function in thrombolytic diseases. Here, PF4 is linked to COVID-19.