Thread by @chrischirp

A conversation with @adamhamdy prompted me to look at how different home nations are dealing with reinfections (people testing positive with Covid more than once, at least several weeks apart)

There are differences that will matter more over time as Covid keeps going 1/7

England only counts the *first* time someone tests positive. So if I tested positive last summer and then tested positive again now, I'd only appear in last summer's numbers.

This means England is undercounting cases (but not by much as long as reinfections are rare) 2/7

Wales *does* allow for reinfections as long as they are 6 weeks apart. So if I tested positive last summer and again today, I would count as a Covid case twice - once last year and once again this year. 3/7

N Ireland does (I think) the opposite of England - it only counts one positive test per person but uses the most recent instead of the first. So if I tested positive last summer and again today, I'd appear in today's numbers and be removed from last summer's. 4/7

Scotland is a bit unclear. They say that cases are all "new positive tests" but positivity rates only use the *first* positive test (ie reinfections not counted).

I think it's likely they do what England does but please someone correct me if I'm wrong! 5/7

Overall this means that Wales includes more cases than Eng & Scot. NI includes more *current* cases (at cost of removing some earlier ones).

Reinfection so far seems rare (ONS from June & PHE), so hopefully not skewing below chart too much, but it will get more common. 6/7

Assuming Covid keeps circulating for a long time & we keep tracking cases & admissons, we should routinely start counting reinfections.

Wales' approach seems pretty sensible to me.

Welcome others' thoughts! /END

PS sources here
E: coronavirus.data.gov.uk/details/cases?…

W: public.tableau.com/app/profile/pu…

NI: app.powerbi.com/view?r=eyJrIjo… (key terms)

S: gov.scot/publications/c…