Thread by @petermbenglish

I keep seeing articles commenting on whether we are entering a new "wave" of Covid-19.

I don't think there is any clear, official definition of a "wave". It's simply a description of what you see on a graph of [something] over time.
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I'm not sure how useful the concept of "another wave of Covid-19" is, now.
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Before saying there is a "wave", you need to be clear: what is it a wave of? (What is the y axis measuring?)

It may seem obvious, but is it? What are we concerned most about? Deaths? Overwhelming the health service, in which case it might be hospital or ICU admissions?
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Or cases?

It used to be that a proportion of all cases would be hospitalised, and a smaller proportion would die; and the proportions were higher with increasing age.

It still is the case; but vaccination has affected it.
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As we have vaccinated so many older and more vulnerable people, the proportion who get symptoms, significantly ill, require hospitalisation or critical care, or who die have shrunk.
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So we could have another distinct "wave" of infections without having a very significant wave of hospitalisations or deaths.
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So, if you read an article about the likelihood that we are about to experience or already in another "wave", ask yourself what the person using the expression means.
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And if you refer to eg "another wave of Covid-19" yourself, make sure your listener's understanding of the term is the same as your own.
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You can find a threaderapp version of this thread at threadreaderapp.com/thread/1399709…, and a slightly tidied-up version as a blogpost at peterenglish.blogspot.com/2021/06/what-i…