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Why Are Vaccinated People Getting Covid-19?
Base rates, denominators, and some really basic epidemiological maths
As the world slowly limps forward from the battering of a global pandemic into a post-vaccine world, there’s a common, and very understandable question being asked across the globe. Why, if vaccines work, are we seeing more and more people getting sick after being immunized against Covid-19? Shouldn’t we all be protected now that we’ve been jabbed in the arm?
And if you look at the figures, it’s absolutely true — in many places where lots of people are vaccinated, most coronavirus infections are among people who have been immunized. This seems to contradict the well-demonstrated fact that vaccines prevent up to 95% of symptomatic disease, and are incredibly effective at stopping you from getting Covid-19.
What’s going on here? Allow me to introduce you to a simple cognitive twist called the base rate fallacy, and go back to the First Commandment of Epidemiology: Thou Shalt Always Remember The Denominator.
