英国药监局（MHRA）4月7日指出，有79人注射牛津疫苗后出现血栓，并发血小板降低，其中女性约占2/3。其中有19人因血栓死亡。死者年龄18-79，其中50岁以下有11人，30岁以下有3人。药监局怀疑疫苗与血栓有一定关联，具体血栓发生机理不清楚。考虑到已经有2千万剂疫苗的注射量，血栓发生率非常低。
腺病毒感染宿主细胞有选择性，一些种类的腺病毒以细胞膜上的 CD46 蛋白为受体进入细胞。J&J 疫苗采用的腺病毒载具Ad26, 牛津大学和AstraZeneca 公司的腺病毒载具ChAdOx1，都是以 CD46 为受体。J&J的载具原型是一种人体腺病毒，英国牛津的载具原型是人工修饰过的黑猩猩腺病毒。
膜蛋白 CD46 可抑制补体激活。补体是一种非特异性免疫保护系统，与细胞裂解和血凝/血栓关系密切。CD46广泛存在于人体细胞。如果没有 CD46，补体系统活性升高，容易血栓。觉得牛津疫苗可能通过 CD46，而与血栓有关联。
参看
MHRA issues new advice, concluding a possible link between COVID-19 Vaccine AstraZeneca and extremely rare, unlikely to occur blood clots， https://www.gov.uk/government/news/mhra-issues-new-advice-concluding-a-possible-link-between-covid-19-vaccine-astrazeneca-and-extremely-rare-unlikely-to-occur-blood-clots
Adenovirus Serotype 26 Utilizes CD46 as a Primary Cellular Receptor and Only Transiently Activates T Lymphocytes following Vaccination of Rhesus Monkeys， https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3457266/
Vector-Based Vaccines Come to the Fore in the COVID-19 Pandemic, https://www.the-scientist.com/news-opinion/vector-based-vaccines-come-to-the-fore-in-the-covid-19-pandemic-67915
News & Views: Getting Familiar with COVID-19 Adenovirus-replication-deficient Vaccines, https://www.chop.edu/news/news-views-getting-familiar-covid-19-adenovirus-replication-deficient-vaccines
Complement Activation on Platelets Correlates with a Decrease in Circulating Immature Platelets in Patients with Immune Thrombocytopenic Purpura，https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5004348/