腺病毒新冠疫苗 · 血栓

英國藥監局（MHRA）4月7日指出，有79人注射牛津疫苗後出現血栓，並發血小板降低，其中女性約占2/3。其中有19人因血栓死亡。死者年齡18-79，其中50歲以下有11人，30歲以下有3人。藥監局懷疑疫苗與血栓有一定關聯，具體血栓發生機理不清楚。考慮到已經有2千萬劑疫苗的注射量，血栓發生率非常低。

腺病毒感染宿主細胞有選擇性，一些種類的腺病毒以細胞膜上的 CD46 蛋白為受體進入細胞。J&J 疫苗采用的腺病毒載具Ad26, 牛津大學和AstraZeneca 公司的腺病毒載具ChAdOx1，都是以 CD46 為受體。J&J的載具原型是一種人體腺病毒，英國牛津的載具原型是人工修飾過的黑猩猩腺病毒。

膜蛋白 CD46 可抑製補體激活。補體是一種非特異性免疫保護係統，與細胞裂解和血凝/血栓關係密切。CD46廣泛存在於人體細胞。如果沒有 CD46，補體係統活性升高，容易血栓。覺得牛津疫苗可能通過 CD46，而與血栓有關聯。

參看

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/