The most important coronavirus number to watch in South Africa
Health Minister has announced the total number of confirmed COVID-19 cases in South Africa is 2,415 – a daily increase of 143.
While the total number of COVID-19 cases in South Africa is interesting, the average number of daily coronavirus cases is actually the most important figure.
The decision to extend or to end the lockdown will be based on the average number of daily coronavirus cases between 10 and 16 April.
Professor Salim Abdool Karim, chairperson of Health Minister Zweli Mkhize’s COVID-19 advisory group, said this figure, which relates to community transmissions, must be closely monitored over the next week.
Karin explained that in the week before President Cyril Ramaphosa declared the state of disaster, South Africa only had 2 new cases per day on average.
This rapidly increased to 21 and 110 cases in the two weeks following the state of disaster announcement.
In the two weeks after the lockdown was implemented, the average daily number of cases declined to 76 and 67 respectively.
The chart below shows the average daily cases for the past 6 weeks. Week 6 is from 10-16 April and will therefore only have an accurate measurement after the data for 16 April is released.
Average number of daily cases, and R zero
Karin explained that when there is a new coronavirus case today, it reflects an infection from two weeks ago.
The decline after the lockdown started, therefore, reflects the positive effect of the measures which were implemented two weeks ago as part of the state of disaster.
He said the coming week is critical. This is because we need to know what the level of community transmissions are after the lockdown started.
“We want to use this information to guide us on what next steps to follow and how we should manage the lockdown,” said Karim.
He said by 18 April they will know if the interpretation is correct that community transmissions have been kept low.
He explained that there were, on average, 67 new coronavirus cases in South Africa over the past week.
The 95% confidence interval is 45 to 89 cases per day. “The true number of cases is therefore somewhere between 45 and 89,” he said.
These numbers provide them with an objective way to assess how many people an infected person is spreading the virus to – also known as R zero.
R zero, known as the basic reproduction number, should be kept below 1 for the infections to decline. This is the government’s aim.
Criteria for lockdown
Karim said through R zero, they have an objective epidemiological criterion for the lockdown.
He gave four scenarios for the average number of daily cases between 10 and 16 April.
- Equal to or above 90, then the lockdown continues.
- 45 to 89 and the positivity to screening ratio (CHW) is above 1 in 1,000, then continue the lockdown.
- 45 to 89 and the positivity to screening ratio (CHW) is equal to or below 1 in 1,000, then ease the lockdown.
- Below or equal to 44 then ease the lockdown.
Karim explained that this set of criteria gives South Africa clear guidance on how to deal with the lockdown.
He said people can expect large daily variations in the number of cases. Instead of focusing on these daily numbers, people should look at the average daily number of cases over a week.
Karim warned if the lockdown is ended abruptly, South Africa runs the risk of a sudden increase in infections.
He advised a systematic easing of the lockdown over several days to reduce the risk of rapid transmissions.
Current situation
The chart below shows the average number of daily cases between 10 April and 14 April.
The red line, at 90 cases, is when lockdown should continue. The green line, at 44 cases, is when lockdown should end.
At this stage, the average number of daily cases for the week is at 96.2 – above the 90 mark that indicates the lockdown should continue.
If this number does not decline over the next few days, the lockdown should continue based on Karim’s guidelines.
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