on Astra and clots

A tribune this morning in The Guardian by David Spiegelhalter on having no evidence that the Oxford/AstraZeneca vaccine causes blood clots.

“It’s a common human tendency to attribute a causal effect between different events, even when there isn’t one present: we wash the car and the next day a bird relieves itself all over the bonnet. Typical.”

David sets the 30 throboembolic events among the 5 million people vaccinated with AstraZeneca in perpective of the expected 100 deep vein thromboses a week within such a population. Which coincides with the UK’s Medicines and Healthcare Products Regulatory Agency statement that the blood clots are in par with the expected numbers in the vaccinated population. (The part of the tribune about the yellow card reports, based on 10 million vaccinated people, reiterates the remark but may prove confusing to some!) As for hoping for a rational approach to the issue,  … we would need a different type of vaccine, far from being available! As demonstrated by the decision to temporarily stop vaccinating with this vaccine, causing sure additional deaths in the coming weeks.

“Will we ever be able to resist the urge to find causal relationships between different events? One way of doing this would be promoting the scientific method and ensuring everyone understands this basic principle. Testing a hypothesis helps us see which hunches or assumptions are correct and which aren’t. In this way, randomised trials have proved the effectiveness of some Covid treatments and saved vast numbers of lives, while also showing us that some overblown claims about treatments for Covid-19, such as hydroxychloroquine and convalescent plasma, were incorrect.”