AZ/J&J Blood Clotting Events
What kinds of clots are we dealing with
They are not due to thickness of blood per se, but related to an immune response (read on for specifics). Antibodies cause the platelets to clump together, which leads to clots.
They are called Vaccine-induced Prothrombotic Immune Thrombocytopenia (VPIT), which is a new term. [1,2]
Vaccine-induced => self explanatory.
Prothrombotic => happens before the formation of the actual clots.
Immune => denotes the involvement of the immune system. Thrombocytopenia => thrombo(clot)-cyto(cells)-penia(lowering) because the free platelet count drops.
It is currently hypothesised to be related to heparin-induced thrombocytopenia (HIT) which was discovered in the 1960s. [3]
These immune reactions appear to manifest as cerebral venous sinus thrombosis (CVST) (i.e. people get blood clots in the sinuses that drain blood from the brain: BAD).
Why do they happen
Auto-antibodies (antibodies against something that is part of one’s own body) against a protein (platelet factor 4) that promotes blood coagulation. [4,5]
It’s speculated that it’s related to the adenovirus vector used in the vaccine binding to platelets, but for now it is unclear. mRNA vaccines have not shown any indications that they might cause something similar.
What is the incidence of these clots
AZ/Oxford:
Germany has reported 31 cases of CVST (29 women) but only 19 of those could possibly be VPIT (i.e. showed reduced platelet levels). 9 patients died. 2.7 million people have been vaccinated. [6]
J&J: 6 cases of CVST in ~1.4 million vaccinations. Can’t find any info on how many had thrombocytopenia (i.e. could actually be related to the vaccine).
Women between 20 and 50 years old seem to be overrepresented so there might be a link there. However, no higher risk groups have yet been identified for HIT. [7]
What is the background rate
Seems to be lower than the rate of incidence we are seeing with vaccinated cohorts. [8]
Is there treatment?
Yes, though it’s important to identify the condition as the typical treatment would be heparin administration (anticoagulant), which in this case would make things worse. [9]
Should all vaccinations be halted?
Given the much higher rate of horrible complications from contracting COVID-19, it would not appear warranted. Rather having knowledge of these extremely rare side-effects and how to treat them, along with figuring out which patient profiles are at highest risk seems to be the most reasonable response.
Stopping administration leads to accusations of allowing the pandemic to rage on. Continuing administration and accusations of not caring about side-effects inevitably surface. From PR standpoint it is a lose-lose.
References
- https://www.sciencemag.org/news/2021/03/rare-clotting-disorder-may-cloud-worlds-hopes-astrazenecas-covid-19-vaccine
- https://twitter.com/SharkawyMD/status/1378147622997929984
- https://en.wikipedia.org/wiki/Heparin-induced_thrombocytopenia
- https://www.nejm.org/doi/pdf/10.1056/NEJMoa2104840?articleTools=true
- https://blogs.sciencemag.org/pipeline/archives/2021/03/30/blood-clots-and-the-az-vaccine-revisited
- https://twitter.com/kakape/status/1376859903030071301?s=20
- https://blogs.sciencemag.org/pipeline/archives/2021/04/14/vaccine-side-effects-q-and-a
- https://twitter.com/jeremyfaust/status/1382536833863651330
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4757158/
