Sunday, April 12, 2020

COVID-19 models for Ireland, Italy and US - 11 April

Thanks again for all the positive feedback on this work.

In this week's update we have included data to 11 April for each region.  The structure of the predictive model is the same as before, with the additional calculation of deaths from the outbreak now included.  We have also simplified and we hope improved the workflow for application to other regions, by replacing the manual adjustment of an 'imposed' population mixing profile with use of the Dynochem Fitting window to fit a 'piecewise-linear' mixing profile to all case data (second scenario in the model).

The models (available here) fit very well to both cases and deaths in each region (first scenario for initial period and second for the outbreak to date).  The now usual caveats apply about known coronavirus case numbers: they lag and obscure real case numbers and their meaning varies depending on the testing criteria, volume and delay in each region and over time. Case data for Ireland has been muddled in recent days by the addition of results from swabs taken over the last month that took several weeks to test; we have attempted to reconcile this unhelpful number over the relevant period and refitted parameters for Ireland on that basis.

Each region's degree of control over the outbreak may be assessed by the current effective 'R', taking account of its original value (R0) and the restrictions.  R_effective should be near or preferably below 1 before restrictions can be safely relaxed for a short period (when it will rise).

The are many 'peaks' in such an outbreak and to say 'it has peaked' requires a more specific definition of the type of peak.  While infection rate may already have peaked (in the first wave), detection lags that, so peaks later; death rates also lag and peak later again.

Various peaks that occur in an outbreak like COVID-19, using model data for Ireland as an example.  Natural time lags as well as testing delays may cause peaks in infection, detection, death (on secondary y-axis) and ICU bed occupation rates to occur at different times.

As usual in the graphs below, discrete symbols are measured data (cases and deaths) and curves of the same colour are model predictions of those data.  'Mixing' reflects the reduced interaction of the population with each other.


Ireland: Including the burst of old case data results received this week, Ireland looks to have a little further to go before the first wave of the outbreak places peak demand on health services.  In order to bring that peak into April, the public will need to observe restrictions more tightly than at present.  Estimated current R_effective=1.1.  The peak infection rate may have occurred around 3 April.


Italy: The first wave of the outbreak has recently passed the point of peak demand on health services. Peak infection rate was probably around 19 March. Estimated current R_effective=0.97.

United States (as a whole):

US: Peak infection rate may have occurred in early April.  Peak demand on the health services could be in late April or early May.  R_effective appears similar to Ireland at approximately 1.1.

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