Thread by @ProfColinDavis

Order has been restored, and the link between cases and hospital admissions seems to be re-established. But this still leaves the puzzle of what happened in the middle of July, when cases and admissions briefly became unstuck.

On this graph, the black line shows the number of cases we'd expect, based on the number of (subsequent) admissions. The actual number fits the prediction (postdiction, technically) very nicely, except in the circled area.

The puzzle isn't what caused the spike. Pretty much everyone seems happy to lay the blame on football (people watching in groups indoors).

The puzzle is twofold:

1) Why didn't the case spike produce an admissions spike?
2) How did the spike dissipate so quickly without a trace?

I think most will explain (1) by saying the spike was among young people, who are less likely to be hospitalised. Which is fine, but young people were already most of the cases (and they do sometimes get hospitalised), so I'm not entirely satisfied by that explanation.

But (2) seems even more mysterious. It's as if everyone who watched football and got infected immediately quarantined. But surely, in practice, many of them went home or to work etc and infected others before they quarantined? Why don't the normal rules of transmission apply?

Anyway, I think this is a puzzle that is of more than academic interest, because it may have implications for how we avoid outbreaks when there are future event-related spikes.

There were some comments/queries about testing. As far as I can see, there wasn't anything unusual about testing over the critical period (test data always show the same periodicity, with dips on Tuesdays and Saturdays).