Histological and functional exploration of platelet activity post-SARS-CoV-2 vaccination

The rapid spread of SARS-CoV-2 prompted swift deployment of early-stage vaccines. These vaccines were crucial for controlling the infection, but concerns about adverse effects, particularly thrombotic complications, arose. One major issue was the potential impact of vaccination on platelet activity. Conflicting findings in the literature, caused by differences in methodologies and platelet activation markers, contributed to uncertainty regarding the risk of thrombus formation after vaccination. This study aimed to assess platelet activity before and after SARS-CoV-2 vaccination to evaluate thrombotic risk. Platelet function was analysed in vitro, using aggregation assays and histological examinations of platelet spreading. Key metrics, including adhesion, surface area coverage, and actin cytoskeletal changes, were measured upon platelet exposure to fibrinogen. Platelet aggregation was also assessed using agonists, like collagen, ADP, epinephrine, and ristocetin. Platelet aggregation was influenced by ADP, epinephrine, and ristocetin in both pre- and post-vaccination samples. Analysis showed reduced platelet adhesion and spread area. However, actin cytoskeletal analysis revealed a post-vaccination increases in stress fibres and actin nodules, attaining a maximal response similar to pre-vaccination levels. The study identified modulation of the platelets to become active, but no significant correlation of platelet activity changes leading to a higher incidence of thrombotic events was found.