Why the concern about vaccine blood clotting?
The AstraZeneca vaccine causes an unusual blood clotting syndrome in about 10 out of a million recipients, and it’s not entirely clear whether the J&J vaccine also does and at what frequency. Those are small numbers, compared to other risks. In particular, if you’re in a country with Covid, they are small compared to the risk of getting Covid and having some serious harm as a result. So why has there been so much concern?
There are a few components to the concern, but one underlying commonality: the clotting is unexpected and poorly understood. Patients turn up with blood clots in unusual places and a shortage of platelets (which you’d normally think of as going with not enough clotting). Some obvious treatments — a standard anticlotting drug (heparin) or a transfusion of platelets — are likely to make things worse, so doctors need to know. There isn’t a really compelling model for how the vaccine causes the problem.
If the risk is 10 in a million, taking the vaccine would still be way safer than not taking it, but a lot of the concerns prompting further urgent investigation would have been whether it’s really only 10 in a million, since we don’t understand (in any detail) what’s going on
- have we missed a bunch of cases — remember that initially the risk was thought to be only about 1 in a million?
- are these just the most serious cases, the tip of the iceberg, with many more milder, but still serious, cases that haven’t been noticed yet?
- are these just the earliest-developing cases, with many more on the way?
- is this a batch problem, with some batches of vaccine potentially having a much higher risk?
- does the problem occur in an identifiable small group of people, who would thus be at much higher risk?
There’s been enough data and enough time now to start being confident that the answer to all these questions is ‘no’. One might rationally prefer the mRNA vaccines, which don’t have this problem, but if you live somewhere with an active outbreak and the choice was the AZ vaccine now or the Moderna vaccine in a month or two, the clotting risk shouldn’t change your decision — and the fact that it wasn’t kept secret should be reassuring.
Thomas Lumley (@tslumley) is Professor of Biostatistics at the University of Auckland. His research interests include semiparametric models, survey sampling, statistical computing, foundations of statistics, and whatever methodological problems his medical collaborators come up with. He also blogs at Biased and Inefficient See all posts by Thomas Lumley »
Thanks Thomas,
However, as this is a statistics blog I’d expect to see your statistical analysis of the ‘enough data and enough time’, to back up your claims- otherwise you are simply another pro vaccine ‘reporter’.
4 years ago
If you’re actually interested, I suggest you start with the European report via this thread by Hilda Bastian: https://twitter.com/hildabast/status/1380045454302273537
4 years ago
The irony of referring to a Twitter account cannot be lost on you surely…and yes I am ‘actually interested’ and did take a look. What I saw were ‘comments’ from Bastian. Is it not ok to ask for peer reviewed academic papers or analysis and research of data these days; or are we to just ‘accept’ what certain academics tell us? What ‘European report’ are you referring to?
4 years ago
What she does take from the document( link seen) is that there are a lot of hypothesise and “…So. No answer here. Just a mystery that needs to be solved. And a very long to do list for investigators. /9”
4 years ago
The AZ vaccine statistics I’d like to see are the first relevant data set in the UK, of the ‘most at risk group’ under 60’s. The MHRA now have this, but have yet to share it with the public. Age group 50-59 were vaccinated from 6th March to around mid-April. The vast majority received the AZ 1st dose as Pfizer was only available as a 2nd dose throughout this period. Will they share the findings of how many severe bloodclot cases were reported specifically in this group? This would be extremely relevant data, with the risk of these events already established, as increasing in the under 60’s.
4 years ago
What she does take from the document( link seen) is that there are a lot of hypothesise and “…So. No answer here. Just a mystery that needs to be solved. And a very long to do list for investigators. /9”
4 years ago
This doctor explain s why he thinks the injection could be in the wrong part of the deltoid for those getting blood clots
https://youtu.be/WuyAtvwP2H4
4 years ago