21 Nov, 10 tweets, 4 min read
Some people have been asking about the ‘models’ I used in this graph to make case predictions beyond today. It’s very simple. There isn’t a model, at least not in the complicated way you might think. Wtf?!? Let me explain.
1\
Instead of using a complex predictive model & having a debate about parameters etc. I just used the case trend/numbers from waves 1 (red) & 2 (blue) after aligning the relative case numbers based on their peaks, as shown. Both waves are similar so this makes sense. 2\
Next, I ‘predict’ the remaining cases in (wave 2) L5 by assuming the trend will match that during the same period in wave 1 (ie the red line between Nov 20 - Dec 4, since I aligned wave 1 from March-June with wave 2 today). This gives the dashed blue line from Nov 20 to Dec 4. 3\
Then, I assume we move from L5 to L3 on Dec 4 and use the L3 case numbers from the corresponding first half of wave 2 (blue line from Sept/Oct) to get us to the end of the year. In other words I assume L3 in Dec will be similar to L3 back in Sept/Oct. 4\
That seems unlikely. Chances are Dec L3 will be worse than Sept L3 but maybe we will have L3+ in Dec? Either way the projection from Dec 4 is likely to be conservative in terms of case numbers but by how much is not clear. 5\
Regardless, this projection through Dec suggests we will exceed 500 cases/day by Christmas Day and 900 c/day by New Year’s Eve, since this occurred in Oct from the same starting point & it led us to L5 on the Oct 22nd. So we should get back to there in early Jan this time around.
We should not forget that this is what might happen and “there is no fate but what we make.” I’m still holding on to the hope that we will do better than this for the remainder of L5 and keep the numbers down more effectively when we lift restrictions.
If we do start to do a bit better again in L5 in then coming days, then extending it to Dec 14 might help to bring baseline cases down lower (<100?), making the now shorter Xmas period safer & perhaps with a huge effort by all this would delay case growth to end of Jan or Feb.
If a vaccine is approved by the EU by mid-Dec then could we see a roll-out beginning from Jan? Would this keep new cases down enough to avoid L5 in 2021? L3 stabilised cases in Sept/Oct but it wasn’t enough to reduce them. Maybe L3+vaccination progress will do it for Q1 2021.
Important to point out, of course, that the above projection for Dec is not so much a serious prediction for what will happen in Dec as it is a very rough guide based on what happened in Sep/Oct. The ‘model’ (such as it isn’t!) is far too simple to be used for real planning.

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# More from @barrysmyth

21 Nov
Query for immunologists...we need about 70% of the pop. to be vaccinated for herd immunity; ie. at 70% we get R=1. So lets call it 3.5m vaccinations. Can we do 500k/month? So this takes 7 months to achieve? What’s the effect of increasing vaccination levels by 500k/mth on R? 1/
In Jan we will be facing the prospect of a further lockdown as cases will be rising fast. If we start vaccinations in Jan then how will this help the R number. If 70% vaccinations imply R~1, then is there a linear relationship between vaccination level and R? 2\
Eg. in early Oct the national R number was about 1.2. If this is our baseline “being careful” rate, and if 10% of the population get vaccinated then does this reduce this baseline rate? By 10% ish? If so will R fall by 10%/mth due to vaccinations, all other things being equal. 3\
20 Nov
Level 5 seems well & truly stuck now, & each day brings a new even higher cases/day ‘prediction’ for an early Dec exit; its now 257 today, up from 223 yesterday. The problem is not only that cases are stalled/rising, but we have less and less time left to fix it before Xmas. 1/
That puts us >500c/d by Dec 25 & >900c/d by Dec 31, but that’s if transmission in Dec is similar to tx in Sept/Oct, which is surely very unlikely. Chances are, it will be markedly worse because of Xmas, so we’ll get more cases later in Dec & need a lockdown in early Jan. 2\
There are 19 counties on the naughty-list tonight (increasing transmission rates, week on week), up from 16 yesterday, including Dublin, and 6 of them now in the upper-right quadrant (high transmission & rising) which likely means further case increases in the coming days.
3 Nov
How are things going in Level 5? Cases and positivity rates are coming down nicely. How does this compare to wave 1 and can this help us to predict where we might get to by December? Let’s have a look ...
(1/n)
I’ve aligned waves 1 & 2 using their peaks. The y-axis is the 7d moving average of daily cases as a fraction of each wave’s peak. Wave 1 peaked at ~872 c/d and came down to about 50 c/d by June. So far, wave 2 has peaked at 1169 c/d & its falling. Where will it fall to?
(2/n)
Next, I (naively) extend wave 2 using the corresponding portion of wave 1; very simple yes, but probably a reasonable, if optimistic, estimate that saves on the modelling.

It suggests that we will get to about 144 cases/day on Dec 4.
(3/n)
2 Nov
Slovakia's drive to test its entire population over 2 weekends got off to a good start on Saturday with 2.5m tested and 1% positivity. Those 25k positives are now in quarantine. A voluntary programme with opt-outs required to quarantine for 10 days.
(1/n)
theguardian.com/world/2020/nov…
Next weekend the second half will be completed and presumably another ~25k positive cases will be found. So approx. 50k people will be in quarantine for 10-14 days. The remaining >5.4m people will presumably be free to go about their business with limited restrictions. (2/n)
There will be false positives among the 50k positives, possibly a fair few of them, but the alternative is that everyone goes into lockdown so this seems like a reasonable trade-off. There will also be false negatives circulating but there shouldn't be too many of them. (3/n)
1 Nov
This seems like an interesting experiment. Slovakia is testing entire population (5m) over 2 w/ends. Testing is ‘voluntary’ but those not participating must self-isolate for 10d. The first round covered 1m people with 1% positivity.
(1/n) @dwnews
In theory, absent issues with false negatives, could an approach like this drive the virus out of a country within a couple of weeks after testing? Imperfect because of false negatives and secondary tx during isolation, but it would surely do more than 6 was in L5 (for all) (2/n)
Eg, assume 1% positive rate from round 1 is correct, then Slovakia will end up with 50k people in isolation for 10-14days after a full testing cycle. After that cases will be the false negatives & secondary tx during isolation. (3/n)
1 Nov
We can now see transmission rates after L3, as we began L5. Much better than start of L3. Almost all counties either in or near the lower-left quadrant (low transmission & falling). A great good from which L5 can do its work if we all do out bit.