Thread by @JamesWard73

Three points as a postscript to the @boardmasters saga:
1. My final estimate of the number of reported covid cases from infections at Boardmasters is just under 9,000 (note this is restricted to the 15-19yo age group, as that’s where there’s a clear signal at regional level) 🧵

2. While the Boardmasters spike was artificially increasing reported weekly case ratios for England last week, it is now artificially depressing them (as last week’s spike is now the baseline we’re measuring against) – note the adjusted orange line is now above the blue.

Without the spike, the case ratio for England would have been almost exactly flat for specimen dates 17th-20th Aug, suggesting an underlying trend with R = 1. So if people tell you English cases are falling, they may be literally correct, but I’d not celebrate too fast.

3. More recently, case ratios for 21st-22nd Aug have gone back above 1 -and note the ratio for 23rd Aug is likely to increase as late-reported cases come in. This *could* be a sign of secondary infections from Boardmasters, but it’s hard to be sure without contact tracing data.

It was inevitable there would be some onward transmission – e.g. as reported here by @TonyNewsCamera. And if R is generally around 1, then our default assumption should be to expect roughly one secondary case for each primary case.

https://twitter.com/TonyNewsCamera/status/1430883311082213384?s=20

– so if we’re keeping the ratio down to 20-30%, that’s still much better than it might have been. At the moment I haven’t got a clear handle on the age breakdown of those secondary cases, because it gets a bit lost in the noise when you go into more detail.

Of course, those secondary cases may lead to further cases, and so on – and so it’s essentially unknowable how many cases would have been avoided if the Boardmasters spike had never happened. But please note that it’s not all bad news, and it’s also very hard to know how many...

…cases will be avoided in the future because those 9,000 teenagers got infected and so will now interrupt transmission chains. As I’ve shown in the past (see thread below), a well-timed spike of infections in low-risk groups, with limited onward...

https://twitter.com/JamesWard73/status/1381708535210344455?s=20

…transmission, can *in some circumstances* reduce the total number of infections and deaths in the long run. I’m not saying that necessarily will happen, just pointing out that the long-term effects could be either positive or negative, and it’s hard to work out which. /end

forgot to mention the regional breakdown of the estimated ~9k infections at Boardmasters, which is: 5k from South West, 2.3k from South East, and about 500 from each of London, West Mids and East of England. handfuls elsewhere. NB analysis does not include Wales, only England.