Thursday 22 April 2021

Clot Flap

On Monday, I made a passing reference to the association between [fatal] blood clotting and some of the Covid vaccines. I have made a plea for clear messaging for public comms on Coronarama: there is a significant [still minority] part of the population who have chugged the conspiracy Koolaid to take up the anti-vaxx flag. It is not an unreasonable stance! Covid-19 is not smallpox or polio or Ebola: it's worse than seasonal 'flu [which no fun] but you can believe that ya ain't gonna die from Covid. But it's not about you, ya dumbass, it's about those older, poorer, blacker people for whom a dose of Covid will be seriously compromising. Not to mention occupying the hospital bed that you will need when you crash your wheels while driving drunk. 

It is entirely right and proper that the FDA, CDC, EMA, WHO [watchdog acronyms all WAA] should take heed of a handful of cases of the same adverse reaction in the days after vaccination for Covid. That's their job: to collate and cross-reference similar events in different hospitals so that the association, if real, achieves statistical significance and something can be done about the issue. It is not okay if there is a pile-on from statistically ignorant, functionally innumerate, journalists with big red headlines implying that we're all gonna die if we get vaccinated [with AZ or J&J]. It was probably inappropriate that several vaccination programmes stopped in a panic - dumping the idea of relative risk. 

Largely because of the insight of Dr Marie Scully [R] UCL Hospital London, it is now clear that there needs to be a minority report for AstraZeneca [and J&J's alternative] vaccination for a really rare interaction between some folks' immune system, the vaccine and a protein called PF4 Platelet Factor 4. Scully is a consultant haematologist and she had seen cases of blood-clotting with low platelet count before. Not often, but in occasional cases after treatment with heparin. Indeed that condition, tho rare, is common enough to have a name: HIT = heparin induced thrombocytopaenia. An itch at the base of Scully's brain called her to test for antibodies against PF4 . . . and bingo! her young just-vaxxed clotee (and then other patients in UK and abroad) tested positive for this antibody. Technical Press Release.

This was really important because until then heparin [a blood thinner] was being used as a therapy for vaccine-associated clotting and the PF4 connexion showed that this was like pouring gasoline on the fire. The PF4-antibody test opens the door to a mechanistic explanation as to why these few handsful of people go down after vaccination. They have a rare genetic background which directs their immune system to work on some aspect of the platelet / clotting cascade as well as delivering a swashing blow to the spike protein of SARS-CoV2.

Should you worry? Not unless you habitually pay idiot tax play the Lotto expecting to win. You are quite likely to get a "normal" blood clot whether of not you get vaccinated and this risk increases steeply with age. It looks like about four PF4 clots will occur for every million people vaccinated - and one of those will die. Normal clots [which are admittedly not as serious as HIT / VIT clots] happen at a rate of about 1/1000. An informative comparison by BBC's More or Less looked at the - clearly acceptable - risk of blood clots associated with the contraceptive pill: 4/10,000 or about 100x worse than the show-stopping clots associated with AZ and J&J vaccines. Getting preg also has a significant risk of adverse clotting events. As I wrote on Monday, this is why they are pushing the AZ vaccines off on Elders because for them the balance of risk clot vs covid leans one way. Prof. Kingston Mills thinks this is emphatically wrong. There is, at the moment, no clotty association with the mRNA vaccines developed by Pfizer and Moderna; so they are better for younger people. Women of child-bearing age find the pill gives them a tangible benefit: not getting a surprise pregnancy. With that same cohort, and their blokey peers, the benefits from a vaccine are fuzzier and more community based. Some people will be involved in a car-crash on their way to get vaccinated the Indian take-away. Many more people don't know feel the difference between a million and a billion.

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