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Astra Zeneca vaccine & blood clots. Summary.
Rare form of blood clots plus low platelets. ~60% involve veins of brain. Almost all after 1st dose.
Risk (UK MHRA): 1 in 250,000 people
Risk (EU EMA): 1 in 100,000 people
Risk of dying: 20-25% of people with these clots have died
Rare form of blood clots plus low platelets. ~60% involve veins of brain. Almost all after 1st dose.
Risk (UK MHRA): 1 in 250,000 people
Risk (EU EMA): 1 in 100,000 people
Risk of dying: 20-25% of people with these clots have died
Approximately half of the deaths in the UK (11 of 19) were under age 50.
The benefits of the Astra Zeneca vaccine according to regulators appear to outweigh risks in all except those less than age 30. https://www.bmj.com/content/373/bmj.n931
The benefits of the Astra Zeneca vaccine according to regulators appear to outweigh risks in all except those less than age 30. https://www.bmj.com/content/373/bmj.n931
While blood clots occur at a certain rate in population what is unusual about these clots is the association with low platelets. Platelets help make blood clots & when platelets are low we are at risk of bleeding not clotting.
Low platelets in context of blood clots is unusual.
Low platelets in context of blood clots is unusual.
This type of combination of low platelets and blood clots occurs in unique conditions in medicine: some patients exposed to heparin. It can also occur with hemolytic uremic syndrome, thrombotic thrombocytopenic purpura, and sometimes with antiphospholipid antibody syndrome.
It is the unusual location (veins of brain and veins draining the bowel) and the occurrence in conjunction with low platelets that makes these vaccine related clots suspicious for a true association. And a scientific puzzle.
There is new data emerging that the mechanism of the clots may involve antibodies generated (presumably by the vaccine) that target platelet factor 4 (PF4), similar to the process that happens in some people after exposure to heparin. @NEJM https://www.nejm.org/doi/full/10.1056/NEJMoa2104840
Similar findings were also reported in a separate case series.
In both series all patients had antibodies to PF4. @NEJM https://www.nejm.org/doi/full/10.1056/NEJMoa2104882?query=featured_home
In both series all patients had antibodies to PF4. @NEJM https://www.nejm.org/doi/full/10.1056/NEJMoa2104882?query=featured_home
Knowing the mechanism has significant implications:
-we may be able to identify who is at risk
-potentially develop a screening test to identity people who should get a different vaccine than Astra Zeneca
-monitor for and treat clots better to prevent deaths.
Making progress
-we may be able to identify who is at risk
-potentially develop a screening test to identity people who should get a different vaccine than Astra Zeneca
-monitor for and treat clots better to prevent deaths.
Making progress
Note that the Astra Zeneca vaccine is not approved in the US. But it is one of the most important vaccines for most of the world. As such the risk benefit decisions made by regulators in each country & how they are clearly communicated to their citizens is incredibly important.
Since COVID itself has been associated with blood clots as well as central venous sinus thrombosis (see below), it is possible that antibodies we generate against the spike protein (natural infection or vaccine) cross reacts with PF4. Hope we have data on precise mechanisms soon. https://twitter.com/vincentrk/status/1372687875863625729
Why this occurs with Astra Zeneca and not with Pfizer/ Moderna is unclear and may be related to the specific epitopes involved.
