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B cell surrounded by antibodies (Image credit: Getty/CHRISTOPH BURGSTEDT/SCIENCE PHOTO LIBRARY)

德国的一个研究小组提出了可能的解释,为什么AstraZenecaand约翰逊和约翰逊COVID-19 vaccines sometimes trigger rare blood-clotting events. But not all experts are convinced the explanation is correct.

The group, led by Dr. Andreas Greinacher, head of the Institute of Immunology and Transfusion Medicine at University Hospital Greifswald, suggests a chain reaction that involves a preservative and certain proteins in the vaccines may be responsible for the rare blood clots.

只在th团队已经完成了相关的研究e AstraZeneca vaccine and recently began examining the Johnson & Johnson vaccine,The Wall Street Journal reported。However, Greinacher said he suspects that the mechanism that causes the rare血液clots may be common to both shots, as both vaccines use modified腺病毒as their means of getting the vaccine into the body's cells,Webmd.reported在四月份。

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"My assumption is, and that's a hypothesis, that this is a class effect of vaccines using adenovirus," Greinacher told reporters during a call on April 20, WebMD reported.

腺病毒是一种病毒家族,通常触发人类常见感冒的症状,但在疫苗中使用,科学家们改变病毒,以便感染细胞,Live Science previously reported。相反,病毒只是充当血管将疫苗成分携带到身体中。(Johnson&Johnson疫苗使用称为AD26的人类腺病毒,而Astrazeneca疫苗含有一种自然感染黑猩猩的腺病毒。)

除了Astrazeneca和Johnson&Johnson Shots之外,Cansino生物学在中国和俄罗斯卫生部的Gamaleya研究所的Covid-19疫苗含有改良的腺病毒,Live Science previously reported。然而,期刊涉及后两种疫苗与任何不同寻常的血液凝血事件没有联系。

And it's important to note that, even with the former two vaccines, the observed clotting events are quite rare: In the U.K., for example, 168 cases of blood clots had been reported by April 14 in connection to the AstraZeneca vaccine, after more than 21.2 million doses had already been administered there,according to Cosmos。截至周三(5月12日),美国报道了28例罕见的凝血障碍与约翰逊和约翰逊疫苗相关,超过900万剂量给药,纽约时报报道

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也就是说,“了解凝血的原因是下一代疫苗的最重要性,因为[新颖]冠状病毒将与我们留下来,疫苗接种可能会成为季节性的,”Eric Van Gorp博士,教授德拉斯兰大学在荷兰领导一批学习凝块的科学家,告诉期刊。

How the shots might cause clots



Once inside the body, the vaccine comes into contact with platelets, the small blood cells involved in clotting, the group concluded in a study posted April 20 to the preprint databaseResearch Square。暴露于疫苗及其相关蛋白质“激活”血小板,使它们改变形状并发送化学信号以提醒免疫系统。活化的血小板还释放出一种称为血小板因子4(PF4)的物质,其通常有助于调节体内的血液凝固。

However, in some instances, PF4 latches onto components in the vaccine, likely some of the cell-derived proteins, and forms large "complexes" that the immune system mistakes as a threat, like an invasive bacterium. That causes immune cells to build new antibodies to attack PF4, triggering a violent immune response.

"Imagine this is like a dragon in the cave who was sleeping for a long time [but] which now got alerted by someone's throwing a stone on it," Greinacher said on the April call, according to WebMD.


With the "dragon" awake, EDTA enters. The preservative causes "leakage" in blood vessels near the injection site, at least in mice, the team found, andpast studiesalso suggest that EDTA increases the permeability of blood vessels. Leaky blood vessels may release the PF4 complexes into the bloodstream and set off a body-wide reaction, the team hypothesized.


However, Greinacher is still working to confirm his theory. "[Greinacher's] hypothesis could be right, but it could also be wrong," Dr. John Kelton, a professor at McMaster University in Ontario who helps run Canada's reference lab for assessing patients with blood clots after vaccination, told The Wall Street Journal. Kelton and his colleagues were able to replicate some of Greinacher's findings but could not confirm the underlying cause of the blood clots.

其他研究组织提出,随着过去的病毒系列与过去的血液凝固有关,携带疫苗的腺病毒壳可能是一个因素。Van Gorp的小组已经理论上,凝血凝块可能会源于镜头后体内炎症的尖峰。

Still others have suggested that the shots may mess with the so-called complement system, a part of the immune system that helps to clear away pathogens and infected cells from the body,Science magazine reported。The spike protein — a structure that sticks off of thecoronavirus- 可以与血管衬里绑定并激活这种补充系统,在某些人中,这可能导致补体系统攻击血管本身。

更多的research will be needed to know for sure. Read more atWebmd.andThe Wall Street Journal