~3.2 million https://abs.twimg.com/emoji/v2/... draggable="false" alt="🇬🇧" title="Flag of United Kingdom" aria-label="Emoji: Flag of United Kingdom"> people may now have #COVID19

~4.7% or 1 in 21. ~10% in London

Assume: 2,822 dead (hosp +20%); IFR 1%; Adj. days to death ~18

So ~282k were infected 18 days ago
~5 days to double so ~3.6 doublings since

So infections to date: ~3.4m, ~6% recovered so ~3.2m now https://twitter.com/DHSCgovuk/status/1245337119721230340">https://twitter.com/DHSCgovuk...
Whole model is v.sensitive to inputs, so low confidence + wide ranges apply.

More deaths --> more infections
Higher IFR% --> fewer infs (don& #39;t need as many for same deaths)
Longer days to death --> more infs (more time to double)
Higher doubling rate --> more infs
Main changes:
- Added 20% on top of hospital deaths to estimate total deaths (ONS)
- Increased IFR from 0.9% to 1% to align with new Imperial work + potential ICU stress
- Increased days to double to 5 assuming lockdown helping to slow (UK deaths 3, UK cases 4.5, Italy now 8-11)
If we were doing population sample testing (as promised here) https://gov.uk/government/news/testing-for-coronavirus-covid-19-will-increase-to-25-000-a-day
we">https://gov.uk/governmen... could observe the infection doubling rate.

We could do this tomorrow using a single day& #39;s testing capacity.

As nothing has been done/published, we& #39;re left extrapolating from deaths.
This would imply total UK death toll of ~35k...

But only if IFR remains 1% + we see zero new infections.

Sadly, neither of the above are sound assumptions.

If our ICU capacity is overrun, the IFR% will spike hard.

New infections depends on hard #Lockdown + test/trace.
A wave is crashing over our ICUs.

We can& #39;t reduce the size of that wave because it& #39;s caused by infections from 2-5 weeks ago.

We can improve our readiness by scaling ICUs + protecting NHS staff.

We can stop the wave getting bigger + longer by hard #Lockdown + test/trace.
A more optimistic view? If #Lockdown has already helped slow infection doubling over last 3 weeks to every 6 days, takes # infections down to ~2.1m.

Still projects 24k death toll assuming ICUs not over-run and zero new infections from today.

Neither are sensible assumptions.
It& #39;s tempting to think... "There& #39;s 2822 deaths and #Covid19 kills about 1 in 100, so there must be ~282k infections".

The problem is you& #39;re nearly right. But those ~282k infections were 2-3 weeks ago. That& #39;s how long it takes to kill.

They& #39;ve been doubling every 4-5 days since.
This isn& #39;t the best way of estimating % infected!

We& #39;re waiting for people to die, assuming fatality rate to judge how many infections drove those deaths, then using doubling rates to judge infections today.

A better way? Population sample testing! https://twitter.com/JamieWoodhouse/status/1243875344916111360?s=20">https://twitter.com/JamieWood...
Why is estimating # infected more important than just tested "cases"?

https://abs.twimg.com/emoji/v2/... draggable="false" alt="1⃣" title="Keycap digit one" aria-label="Emoji: Keycap digit one"> Infected people are doing the infecting. The "cases" are mostly in hospital or dead.

https://abs.twimg.com/emoji/v2/... draggable="false" alt="2⃣" title="Keycap digit two" aria-label="Emoji: Keycap digit two"> If you know # infected and # deaths you can assess how deadly this thing really is (IFR%, not just "case" fatality)
https://abs.twimg.com/emoji/v2/... draggable="false" alt="3⃣" title="Keycap digit three" aria-label="Emoji: Keycap digit three"> Telling public % infected helps us comply with hard #Lockdown.

BJ& #39;s speech should have started:

"There are infected people in every train, in every shop, in every park, in every tube... you might even be one of them... please take what I am about to say very seriously..."
This poll shows a dangerous level of complacency across the UK. I suspect this is worse in the real world.

Most people think less than a million are infected! That& #39;s what happens when govt + press only talk about the "confirmed cases" iceberg tip. https://twitter.com/JamieWoodhouse/status/1245291470107672576?s=20">https://twitter.com/JamieWood...
https://abs.twimg.com/emoji/v2/... draggable="false" alt="4⃣" title="Keycap digit four" aria-label="Emoji: Keycap digit four"> "Total infected" tells us how many people are going to be coming through our ICU capacity in the next few weeks and whether that will be overrun.

If it is, #Covid19 will kill much more than 1%. When you run out of ICU beds / ventilators, many more die as in Italy/Spain.
A powerful visualisation of deadly UK #Covid19 complacency:

"Right things... at the right time..."?

H/t @Imperial_JIDEA (I& #39;ll stop my amateur efforts as your weekly reports start to come out - critically important)
You can follow @JamieWoodhouse.
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