When should the current Lockdown finish? How about 3rd April

All the previous charts have simply taken the England in-hospital death rates and plotted them. I have then postulated what the charts might look like if the peaks were reached sooner. Nothing more, nothing less. The following chart depends on two assumptions:

1. The peak of new-infections is 13 days prior to the peak in deaths.

2. The IMR was 0.7% in the spring and 0.4% in the autumn. 

If you want to model all this out properly it would be simply a matter of plotting several charts with different input values and seeing what the charts look like. I have no doubt that part of the expert advice to the government is to run these kinds of numbers and therefore generating a range of potential dates to relax the Lockdown.

(Click on the image to see a bigger version).

There is without a doubt a temporal relationship between new infections and deaths. The exact nature of this relationship is not known for sure but 13 days is a reasonable estimate. It is based simply on the time from initiation of lockdown to peak of deaths (on average). Thus this figure will be reasonable accurate.

The IFR is the Infection Fatality Rate put simply that is the number of people who die as a proportion of the total number who get infected. In principle, it is possible to measure this number directly. In practice that is extremely difficult. In order to do so, you either need to be testing (accurately) the whole population and thus you know the total number of infections (the total number of deaths being a robust figure as well) - or you need a representative cohort that can be followed prospectively to see how many of those who are infected (not necessarily symptomatic) end up dying from Covid-19.

I took the IFR's that I used to generate this chart from here: https://www.cebm.net/covid-19/estimating-the-infection-fatality-ratio-in-england/

This is one of several estimates around. There are lots of caveats with this data. The one thing that is clear (although we'll have to wait for detailed publications on this point) is that,  of those who present with Covid-19, fewer people are dying. We seem to have made several incremental improvements in supportative care such that the mortality from Covid-19 is lower. This is really good news. 

However, in terms of tracking the pandemic, it makes things more complex. If the mortality rate is fixed then using the death rate to track the pandemic is easy. The number of new infections is simply derrived accurately by multiplying the number of deaths by the IFR. If the IFR estimate is wrong it doesn't matter for our purposes here as the key to understanding the pandemic (and how we respond, to this is the timing of the peak. It doesn't directly matter here whether the IFR is 2% or 1% or 0.5% or 0.1% the peak will still correspond to the peak in deaths - just ~ 2 weeks earlier. I.e. if the IFR is constant it changes the numbers but allows east comparison between spring and autumn. If it's not, then an adjustment is needed.

To point of a lockdown is to reduce new infections. (Unless you are able to test everyone or at least a representative cohort then the best way to track new infections is to track back from the death rate. In the Spring of 2020, the only accurate figure we had was the daily death rate). However we know that the IFR is different between the spring and the autumn we just don't know for sure how different.

All I have done here is to use these two figures to estimate infection rates based on the known death rates. The point here is that because the IFR is different the number of infections implied by a death rate of x in May 2020 would be less that the number implied the the same deathrate of x in January 2021.

What I am getting at is that if we assume the relaxation on 30th May 2020 makes sense, then we need to acheive the same level of infection in the community in Feb-April 2021 to relax the current lockdown. The number of daily deaths in Jan '21 appears to be about the same as April '20 but because the IFR is now lower (again this is good news!) it does reflect a much higher infection rate in the community and thus we have further to go to be in a position to relax lockdown.

This is just one chart. There are other ways to derive these estimates and the potential that the estimate of the IFR being wrong is important as that will change the graph and move the target level of ~8000 infections a day to a different point in time and thus change when is the right time to relax the Lockdown.

Two more things need to be said though. Firstly I think ~8000/day is still too high a level to be relaxing. We need to be at a point where the numbers are low enough that Track & Trace can work. So maybe, we need to wait a bit longer?

The other unknown here is the effect of vaccination. The vaccines were passed as safe and effective based on the trials that showed they reduced the risk of people getting ill. That's not the same as saying they stop people from passing the virus on (whilst remaining well themselves). Increasingly we are seeing early evidence that the vaccines are also effective at stopping the spread. As more people are vaccinated, it does become easier to relax restrictions.⁰

Lots of unknowns but based on what we have so far; beginning - middle of April would be my target. If I find more data on IFR estimates which enable me to refine this further and/or fixed estimate on time from infection to death I will modify the chart accordingly.

AFZ

The Night is Dark but the Dawn is Coming...

 Here's an update as to where we are as of 14th February 2021. (See previous posts for details of the methodology).

The horizontal line represents the death rate (and thus by inference a proxy for infection prevalence) when the Lockdown was relaxed in May 2020. This is the earliest it would be safe to relax this Lockdown (I would argue for another week beyond this point). There is one caveat to this that the inferred infection rate may be different in March '21 compared with May '20 as the Case Fatality Rate is lower and thus the death rate corresponds to a higher infection level. Conversely large sections of the population will be vaccinated so it's not clear what the correct point is. However, as always in this pandemic, erring on the side of caution seems very wise.

AFZ

Covid-19 and How Johnson's Government has failed totally and completely.

And thousands have died unnecessarily as a consequence.

 

This post builds on these two previous ones:

http://alienfromzog.blogspot.com/2021/01/covid-data-january-2021.html

http://alienfromzog.blogspot.com/2020/09/covid-19-and-why-timing-of-lockdown.html

In the previous posts I have laid out the caveats that exist around these charts. This is a simple method of estimating the effect of the timings of key decisions but 1) it is in line with much more complex modelling (reference in first post) and 2) it is intuitive and easy to understand: When you lockdown, around 2 weeks later you will see death rates start to fall. Because the growth rates are exponential a week's difference in timing makes a huge difference in the total number of deaths.

In this post I am going to lay out three scenarios. None of which support the government's managment of this crisis. They have failed. Many thousands more people died than needed to. That is the inescapable conclusion of all this. 

Firstly, I will lay out the effect in the Autumn of not learning the lessons of the Spring. This was the major thrust of my post in September - by refusing to acknowledge the mistakes of the past - the government doomed us to the consequences of making the same mistakes again. That is exactly what happened.

Secondly I want to show the effect of acting sooner in the spring - there was a point in mid-march when it was inescapable that prompt and drastic action was needed. It is probably unfair to blame the government for what went before then (in terms of the Lockdown decision-making, although not in terms of PPE planning or other decisions but I am not going to write about that here).

And thirdly I will look at a 'perfect' response. The point here is that the government has claimed - and continues to do so - that the UK government has done an amazing job responding to this 'unprecedented crisis.' In this section I will hold the government to their own standard - this is what was possible if things had been done right from the very beginning. 

For me, the second scenario is, I think, fair criticism. Any government can make honest mistakes and that is a good arugment for using my second model rather than the third as a true comparitor with the sad reality we are living. However, when the government claims to be 'World-beating' or 'proud' of their response, then the honest mistake arugment runs into trouble. The on-going issue is an absolute and total refusal by the government to admit mistakes were made. Without accepting that mistakes were made, it is impossible to learn from them. And the consequence of that is measured in thousands of lives.