There has been some debate about the timing and effectiveness of the lockdown measures adopted by the UK in its response to the Coronavirus pandemic. I’m sceptical about the sense of trying to rewrite the past, but I was intrigued as to what my model’s findings might have been. But, we are where we are, and most energy should be focused on the here and now, and the future. But, no doubt, there are lessons to be learned eventually.
NB Government health warning – this is pure speculative modelling, and it is more about the sensitivities in the setting of modelling parameters, and not a statement of fact! Don’t quote me!
Some commentators and academics (Professor Rowland Kao at Edinburgh University tweeted this BBC coverage of his modelling work for Scotland) feel that the UK might well have applied the lockdown measure 2 weeks earlier, on the 9th March, as Italy did, instead of on the 23rd March. UK Government states that our first cases were later than for other countries, and so too, therefore, was our lockdown. Time will tell how significant this is.
I was interested to see what my model (the Prof Alex de Visscher code, with my parameters, modifications and published data for the UK situation) might have made of this for the UK, and I have run the model for some options.
A major problem with running any model from 9th March for the UK is that the first UK deaths, specifically attributed to Covid-19, on the original basis, prior to the inclusion of Care Home figures, were on the 10th March, although, of course, there had been many more cases of infection reported, with people being admitted to hospital and ICU departments in the hundreds. I’m sure that, as discussed above, there will have been deaths associated with the pandemic, but not officially recorded as such.
My current model forecast
It’s important, first of all, to state my baseline, which is my model’s current forecasts for the pandemic in the UK on the basis of the March 23rd lockdown, which embraced working from home, social distancing, school, restaurant and pub closures and several other measures. UK lockdown did allow for excursions for exercise once a day (not allowed at that time in Spain and Italy, for example), and travel for essential medical supplies and food (possibly to help others with those aspects).
In that baseline work, current as of May 14th, these are the graphical representations of the outlook, which forecasts a little over 42,000 deaths by the late summer 2020, stabilising at about that number into the future, assuming no changes to the 84.1% lockdown intervention effectiveness, and no pharmaceutical intervention yet (either vaccine or radically more effective treatment of symptoms). The orange curve always represents the reported numbers.
My model projection is broadly in agreement with the following projection from the IHME, the Institute for Health Metrics and Evaluation, an independent global health research center at the University of Washington, which forecasts between 43,000 and 44,000 deaths in the UK by the summer.
The number of cases, below, is predicted at 2.8 million in the UK, assuming that only 8% of those with the virus are actually tested and diagnosed, a percentage that is informed by the ratio of deaths to real cases derived from other countries’ experience. The fit of the model, therefore, isn’t as good for cases, as the data is fuzzy. The 12.5 multiple on reported numbers mentioned on the chart takes account of that 8%.
It is likely, therefore, that we are not yet aware of anything like the real number of cases, and even death data is now felt to have been understated, currently attributed by confirmed test diagnoses only, not by a simple mention of Covid-19 on death certificates. These latter figures are now being analysed by Government. My model will be updated (as it has been recently to include Care Homes) when those figures are adjusted, as they surely will be when the data is cleansed. The UK Office for National Statistics are working on this, and have already published some numbers (but with some lag, and so are not up to date).
The UK Government does now report for Care Homes in the “all settings” figures it reports, as of nearly two weeks ago, and it retroactively adjusted all historic reported numbers to take those into account, which my model does too; but the death certificate reference to Covid-19 is still not a factor in assigning deaths to Covid-19 in the official published UK daily data.
It is fair to say that policies on this vary hugely from country to country, and from region to region within countries, so it isn’t easy to see where to draw the line.
Options for parametric sensitivities for the March 9th lockdown scenario
It is hard to be sure what the effectiveness of lockdown measures might have been in early March. Some other countries, such as China, were seen to enforce very stringent measures at (and before) that time (having encountered the Coronavirus earlier) and in his own work, Alex de Visscher has used 90% effectiveness for China. This figure relates to the extent of the reduction in infection rate in the model, 90% effectiveness reducing the rate to 10% of its original value. See my blog article for a description of the model and its variables.
At the other end of the scale, the USA model was set at 71% initially, and Canada at 75%; Italy at 79.1% and Spain at 85% were some other choices. Lots of sensitivities were run around these settings, but this gives an idea of the possible range.
The best fit of my current model, as above, for the March 23rd lockdown is currently for an effectiveness of 84.1%, and it is continuing to match published data at that setting, and therefore remains the basis for my current March 23rd lockdown forecasting.
Without any changes to the underlying infection rates, I ran my 9th March UK lockdown model for three values of interv_success, the model variable for lockdown (intervention) effectiveness; for the current 84.1%, and then for 80% and 75%.
I should say that in the University of Edinburgh work mentioned above, which was for Scotland, information on commuting movements was input to their models, using Google mobility data, to try to get an understanding of how social restrictions affect spread of the virus. They found that “Not moving so far away from one’s home is one of the big impacts of what lockdown is doing”.
I haven’t been able to do such an activity analysis, but the % effectiveness in my model is a reflection of assumptions about that. My feeling is that in the UK, we were, and are, unlikely to be able to enforce lockdown as strongly as China did. In the UK, for the last 6 or 7 weeks, we have, as I mentioned, had more freedoms than, for example, Italy and Spain to go outside for exercise (running or cycling, say).
Our recent relatively high public compliance rate with UK Government directives for lockdown measures (working from home where possible, social distancing etc) might not have been as good earlier on, when the impact of the pandemic here in the UK wasn’t confronting people so directly, or to such an extent, as two weeks later, on the 23rd March, by when 359 people had died, and published case numbers were 6650. These numbers compare with no deaths as of 9th March (on the original basis, without inclusion of Care Homes), and just 321 cases.
I should again emphasise that the reported case numbers might well be understated by a factor of 10 to 15 (12.5 is the figure Alex has worked with), judging by the experience in other countries further down the pandemic track.
Taking all this into account, my other options for interv_success are for lower % impact on the infection rate than works best currently, not higher – the current 84.1%, and then for 80% and 75% as mentioned above.
I present the outcomes in graphical form. The first sets of graphs, for lockdown starting on 9th March, are for these three options for intervention effectiveness.
84.1 % effectiveness (as per my current, well fitted model)
We see here that on the larger chart, presenting the situation up to May 13th, instead of the current reported 33186 deaths (the orange curve), the model would have forecasted 537 if lockdown had happened on March 9th, assuming 84.1% effectiveness, which I think would be too high for compliance at that time. For the forecast long term (top left), deaths would stabilise at just over 600 by the end of summer 2020, with total infections at a little over 40,000.
This time, on the larger chart, presenting the situation up to May 13th, instead of the current 33186 deaths, the model would forecast 717 deaths if lockdown had happened on March 9th, assuming 80% effectiveness. The longer term outcome would be about 1000 deaths with just under 70,000 cases, stabilising in the autumn of 2020.
Finally, on the larger chart, presenting the situation up to May 13th, instead of the current 33186 deaths, the model would forecast 1123 deaths by 13th May if lockdown had happened on March 9th, assuming 75% intervention effectiveness. The long term deaths would be nearly 6000, but with still a few deaths per day even a year later, because of the continuing lower intervention effectiveness (assumed by the model), and cases would have reached a little under 400,000 in a year’s time, with negligible growth by then.
These results show a marked reduction in deaths forecast for May 13th by my model for the March 9th scenario lockdown, compared with the actual March 23rd lockdown results. This is only a model and will have deficiencies in a) the reduced data available for calibration of the model before March 9th (no deaths, for example) for model fitting, and b) the lack, therefore, of a firm basis for setting transmission rates at that time, and testing them.
But it does show the high dependency the later results have on early data.
There is another feature in the numbers, however, that is more noticeable in the charts for the assumed 75% lockdown effectiveness. This is is clearer when we look more closely at the long term outcome for deaths, starting with that 75% case, as above,
where we can see that even in April 2021 (in the absence of pharmaceutical measures, or any change to the intervention effectiveness) the deaths are still increasing (if there were no further increase, the log chart would be flat, i.e. horizontal, at that point). The 5738 deaths at that time are not the maximum.
This outcome is even more stark if I choose 70% intervention effectiveness, and in this case I present both the linear y-axis and the log y-axis charts, since on the linear chart, the numbers are significant enough to be perceived visually. The orange curve is always the actual reported numbers, whatever the model scenario.
70% effectiveness analysis
The linear chart makes clear that by the end of April 2021, there continues to be a high rate of increase of deaths, and, equivalently, we can also see that the log chart is much further from flattening than in the 75% case, even after more than a year of lockdown, at this level (70%) of effectiveness. The modelled number of deaths by April 2021 is over 250,000, with 17 million cases.
Visually, the reported deaths look very unlikely to get anywhere near that, and in my base March 23rd lockdown model (which has a good fit with reported numbers at the moment, May 13th, the orange curve here), deaths are projected to flatten at 42,000, with cases at 2.8 million.
I totally accept that the model will have its deficiencies – the calibration phase to March 9th is short, and the infection rate parameter might not be realistic as a result.
But from a comparative model behaviour perspective, this is another example, in an exponential growth situation (as a pandemic is) that early numbers are not a good indicator of outcomes. Small early differences make very large differences down the track. It’s a non-linear relationship, with high sensitivity of the pandemic growth rate to the % effectiveness of intervention measures (most noticeably at the lower % effectiveness).
It does seem that if the effectiveness of interventions is not high enough, while there can appear to be good early results (the number of deaths by May 13th 2020, in even the 70%, least effective model, is 1,980, as compared with 540 for the 84.1% case above (starting March 9th)) the pandemic eventually overcomes the measures.
By the end of 2020, in this 70% scenario, the modelled deaths are likely already to exceed the reported deaths, and would be growing quite fast by then, as can be seen from the charts.
This tells me that if pandemic intervention measures are to work effectively, and strategically (i.e. long term), they need not only to be early, but also at least at 80% effectiveness in terms of reducing the infection transmission rate for this Coronavirus.
Long term 80% effectiveness outlook
We can confirm this from the 80% effectiveness longer term outlook for the March 9th lockdown scenario (assuming no changes in the lockdown measures, and no available pharmaceutical measures).
At this level of intervention effectiveness (80%), the modelled deaths curve peaks at about 1000, reaching that point by autumn 2020 as stated in the earlier section, with about 67,000 cases by that time, stabilising at 68,000 before a year’s time, as we see in the chart below. Again, the orange line is the current status of the reported cases (x12.5 as before).
This article simply addresses the theoretical, earlier lockdown scenario that has been much discussed. The modelling I have done is probably not adequate in terms of absolute numbers, but it is clear, from comparisons of my scenarios, that on similar assumptions to the current modelling for the March 23rd lockdown initiation, the number of deaths at May 13th would have been less – probably far less, as asserted by the University of Edinburgh study for Scotland.
Whether those assumptions are valid (i.e. that the intervention effectiveness would have been the same) is questionable.
Furthermore, it requires just a 10% to 15% diminution of that effectiveness percentage to lead to a worse outcome in the long term.
I see this as an indicator that, in the absence of pharmaceutical measures (a vaccine, ideally (of lasting effect), or medicines that handle symptoms effectively, and save lives) the intervention measures have to continue to be carefully monitored, including an understanding of which are the most effective at reducing infection transmission rates.
It may well be that as the researchers at Edinburgh stated, the “stay-at-home” policy is the most effective measure, and that trips away from home should continue to be minimised even into the long term, by working from home where possible, and otherwise travelling only for medical and food purchases.
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[…] already modelled the scenario for March 9th lockdown (two weeks earlier) and reported on that in my May 14th and May 25th posts at this blog. The precise quantum of the results is debatable, but, in my […]