Is South Africa getting better at treating COVID-19?

There is a great deal that we can learn from the Western Cape COVID-19 experience.  Not only is the viral propagation most advanced in the Western Cape, but the province also has the richest source of data on COVID-19 hospital admissions.  The graph below compares the daily reported deaths (plotted against the right-hand axis) with the daily reported hospital patients who tested positive for COVID-19 (plotted against the left-hand axis). ICU patients are also plotted against the left-hand axis.

The two surprises from the comparison are (1) that reported deaths peaked before the hospital patients did, and (2) that after the peak the trend for reported deaths is below that for hospital patients.


The next graph compares ICU patients only with reported deaths.  In this comparison, the reported deaths are multiplied by 5 so that the two graphs can be compared on the same axis. The widening gap between daily deaths and ICU patients from 20 June is evident from the comparison.  One explanation for this gap is that ICU survival rates have materially improved since 20 June. What this means for the pandemic in South Africa is hugely encouraging especially if the rate of ICU survival continues to increase.


 I had a look at how this new information might impact on the COVID-19 modelling for the Western Cape.  Two changes were made to the modelling, namely (1) the parameters for hospital treatment were adjusted to better fit the hospital patients data, and (2) the Infection Fatality Rate (IFR) was reduced for the period from 20 June.  The reduction in IFR reflects the improvement in ICU survival.

Refitting the NMG model for the Western Cape with the reduced IFR results in an increase to the forecast for unreported infections.  This means that a greater % of the Western Cape population are forecast to be infected in this first wave of the pandemic.  The updated fit to reported COVID-19 deaths for the Western Cape is shown below:


The new modelling forecasts that between 20% and 25% of the Western Cape population will have been infected by the virus in the first wave of infections.  Could these percentages be getting close to the level at which herd immunity is reached, or where the level at which a second wave of infections will have far less intensity.


27 July 2020




 

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