We would like to share ideas on “Three cases of acute venous thromboembolism in females following vaccination for COVID-19.” Andraska et al concluded that “We present a series of three women who developed venous thromboembolism (VTE) following mRNA-1273 vaccination at a single healthcare system.” Pathogenesis of acute venous thromboembolism is an interesting issue. In the present report, mRNA COVID-19 vaccine is used. The autoimmunity development after mRNA COVID-19 vaccine administration is proposed, and it might be mentioned as a cause of thrombotic disorder. However, if an autoimmune problem is referred to, there should be an identification of problematic antibody. In the present case, there is also other possible pathomechanism. After vaccination, the rapid blood viscosity change can occur and this might cause rheological change. The acute thromboembolism might be the result.