When to end lockdown?
I spent much of the weekend updating the COVID-19 pandemic model so that we can better understand the impact of extending the current lockdown in South Africa, or replacing the lockdown with other intervention strategies to manage the spread of the disease. The revised NMG report and model can be found at https://nmg-covid-19.sctechnology.co.za/.
The modelling demonstrates how difficult it will be to lift or relax the lockdown conditions if South Africa wants to avoid an outbreak of infections. In line with the experience in Europe, the lockdown appears to be an effective mechanism to reduce the spread of the disease.
Research by Imperial College London into the effectiveness of non-pharmaceutical interventions in 11 European countries, showed that lockdown halved the speed at which COVID-19 progresses.
(Self isolation and social distancing were much less effective)
What this does mean is that the speed at which the disease progresses will double should lockdown be lifted completely.
What is still unknown is whether the lockdown will be as effective in slowing down the disease transmission in South Africa's poorer communities. Given the time lag between being infected by the virus and the onset of the disease, and the difficulties with testing in these communities, it may well be some time before we can understand this.
It is then conceivable that the speed at which COVID-19 in transmitted in South Africa will increase, irrespective of whether the current lockdown restrictions remain in place.
The other adaptions made to this release of the NMG model were done to better estimate the infected lives that show symptoms of COVID-19 but go unreported in a population. We do this by using estimates for the Infected Fatality Ratio for the disease and applying these to the reported deaths for the population. The Infected Fatality Ratio is the number of deaths per 100 lives infected with COVID-19, and has been estimated by Imperial College London. The ratio varies by the age of the infected life as follows:
The low number of expected COVID-19 fatalities for lives below age 50 is encouraging.
In 2017, 144 986 of the deaths that occurred in South Africa were between the ages of 20 and 49. This is 0.62% as a ratio of the lives in that age band. It should then be feasible to lift the lockdown for this group? But more on this tomorrow.
15 April 2020
The modelling demonstrates how difficult it will be to lift or relax the lockdown conditions if South Africa wants to avoid an outbreak of infections. In line with the experience in Europe, the lockdown appears to be an effective mechanism to reduce the spread of the disease.
(Self isolation and social distancing were much less effective)
What this does mean is that the speed at which the disease progresses will double should lockdown be lifted completely.
What is still unknown is whether the lockdown will be as effective in slowing down the disease transmission in South Africa's poorer communities. Given the time lag between being infected by the virus and the onset of the disease, and the difficulties with testing in these communities, it may well be some time before we can understand this.
It is then conceivable that the speed at which COVID-19 in transmitted in South Africa will increase, irrespective of whether the current lockdown restrictions remain in place.
The other adaptions made to this release of the NMG model were done to better estimate the infected lives that show symptoms of COVID-19 but go unreported in a population. We do this by using estimates for the Infected Fatality Ratio for the disease and applying these to the reported deaths for the population. The Infected Fatality Ratio is the number of deaths per 100 lives infected with COVID-19, and has been estimated by Imperial College London. The ratio varies by the age of the infected life as follows:
The low number of expected COVID-19 fatalities for lives below age 50 is encouraging.
In 2017, 144 986 of the deaths that occurred in South Africa were between the ages of 20 and 49. This is 0.62% as a ratio of the lives in that age band. It should then be feasible to lift the lockdown for this group? But more on this tomorrow.
15 April 2020
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