evidence: Blood clotting is a well-recognized complication of SARS-CoV-2 infection. It has also been identified as an extremely rare side effect of certain COVID-19 vaccines. The risk with vaccines is exceedingly low and individuals are at a significantly higher risk of developing a blood clot from COVID-19 infection than following COVID-19 vaccination. [...] The Moderna or Pfizer-BioNTech mRNA vaccines have not been shown to increase the risk of blood clots in multiple studies. However, two COVID-19 vaccines are associated with an extremely rare syndrome known as vaccine-induced thrombotic thrombocytopenia (VITT). It was discovered in March 2021 in connection to the AstraZeneca COVID-19 vaccine and then later with the Johnson & Johnson COVID-19 vaccine. In rare cases—2 to 20 per million—antibodies that the body produces as a side effect of the vaccine lead to uncontrolled activation of platelets. This causes both low platelet counts and blood clots to form. [...] If deciding whether a COVID-19 vaccine is worth the risk, Abou-Ismail tells his patients that "mRNA COVID-19 vaccines are safe in patients with a history of blood clots or increased risk factors. The risk of developing a blood clot from COVID-19 infection is far higher than getting a blood clot from a COVID-19 vaccine."