In a very strict mathematical sense, herd immunity is the slowing of disease spread due to sufficient infected people in a population (such that Rt<1)
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This leads to the second definition, which is the ability to calculate immunity within a population based on dynamics of disease spread
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And finally, the common usage that's being bandied around a lot these days - herd immunity to describe a population which is largely immune to outbreaks of an infectious disease due to existing population immunity
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Problem is, all three of these are being combined into a single idea in the popular media, which is not great because only definition 3 results in a somewhat permanent ending to the pandemic
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The
#GreatBarringtonDeclaration, for example, uses the first definition in a very disingenuous way to imply that endemic transmission of the disease (where Rt may at some points be <1) is equivalent to population immunity that prevents outbreaksShow this thread -
If someone uses the term "herd immunity" to describe an actual strategy or outcome from COVID-19, it's worth digging in to EXACTLY what they mean by that term, because often it's very much not what you'd imagine
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And if you're interested in reading more, this article is a great place to start:https://academic.oup.com/cid/article/52/7/911/299077 …
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Also, I made an error in the second tweet - in a strict mathematical sense, herd immunity is having sufficient people IMMUNE to the disease in a population. Infection does not always confer immunity, and you can be immune without infection (vaccines!)
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I think you nailed the problem. It’s allowed the GB to get away with the deception of ambiguity.
Thanks. Twitter will use this to make your timeline better. UndoUndo
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Re: "herd immunity is the slowing of disease spread due to sufficient infected people in a population (such that Rt<1)" Did you mean R0, instead of Rt?
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Nope! R0 is the basic reproduction number in a fully susceptible population, Rt is the time-varying one that changes when people are immune
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