A mini-review on the side-effects of COVID-19 vaccines on Thrombosis with Thrombocytopenia Syndrome (TTS)

In May 2024, the well-known pharmaceutical company AstraZeneca admitted that its COVID - 19 (SARS-CoV-2) vaccine can cause the rare side effect of Thrombosis with Thrombocytopenia Syndrome (TTS), involving blood clots along with a low platelet count. This is a potentially severe condition, with a fatality rate up to 44%. Several studies indicate a link between different COVID-19 vaccines and TTS or VITT (Vaccine Induced Thrombotic Thrombocytopenia), however, a majority of such cases have been reported after the vaccines ChAdOx1 nCoV-19, manufactured by AstraZeneca and Oxford University, and Ad26.COV2.S, made by Johnson and Johnson. Both these vaccines use the same mechanism: modified adenovirus vectors. In these viral vector vaccines, some researchers have theorized that an immune response could be triggered where the body produces antibodies against platelet factor 4 (PF4), a protein involved in blood clotting. Another theory suspects endothelial cells and receptors to have an inflammatory response, causing VITT. Though the exact cause remains unknown, an association between some vaccines and thrombotic events can definitely be discerned by past research, so this article will evaluate different vaccines and their connections with such events.