Thread by @dsymetweets

Exponentials still have the capacity to shock me.

If mass wearing of masks make just 0.01 shift in the spread per day, from say 1.22x to 1.21x, there would now be ~20% fewer cases (and ~20% fewer deaths) in the UK since March 12.

I had to double check that multiple times.

This sort of result should have been hammered into our collective consciousness throughout February and early March. Every little effective intervention, widely adopted, saves many, many lives.

The thing is, that 0.01 difference accrues every single day, afresh - and slightly compounded too. Every day we do a small, effective intervention, we accrue it's life saving effect all over again. Every single day. All over again.

cc @RoryStewartUK

Here is a spreadsheet across a simple three phase simulation, to roughly compare proportionate effect of small or early interventions across first wave. The numbers still shock me.

1drv.ms/x/s!Aq5gXOPBI5…

Mass masking: a 0.01 reduction in spread across all three phases gives ~20% reduction in fatalities in first wave

Early action: If first phase in early March is 1.05x instead of 1.3x, there is ~11x reduction in total fatalities in first wave

Summary: early decisive action and the accumulation of many small interventions are absolutely key. And each small effective intervention makes a huge difference. Exactly the opposite of the rhetoric of @BorisJohnson and @CMO_England in early March.

By far the most likely outcome for CV19 will be stop-and-go suppression until an effective vaccine is achieved.

In each wave, early intervention is key to minimising fatalities, and each small intervention makes a major difference.

It's wrong to use words like "marginal" or "small impact" for interventions for epidemic curves. Any intervention that's slightly effective (eg. -1% spread/day) has disproportionate impact (eg. -20% fatalities) when applied across a 3 month curve. This is not a linear problem.