Understanding the Covid-19 numbers in SA

Calculating the death rate is not as simple as dividing the number of deaths by the number of cases. For example, as of 7 April, 13 deaths in 1 749 cases were reported in South Africa – giving a death rate of 0.74%. But it is much more complicated than that. For one thing, most of the 1 749 people confirmed to have Covid-19 on 7 April were still infected and some of them may still die.

By the time South Africa had its 1 000th case, the country had no Covid-19 deaths. All our deaths have come subsequently. Similarly, Germany also had no deaths when it had its 1 000th case. As time has passed, the death rate in that country has crept up. It’s now about 2%.

What we need to do to wipe out the epidemic is reduce the average number of times an infected person infects another person to below one. Then the epidemic will fade away. The rate of new infections depends on three things:

  • How many people the average person comes into contact with daily
  • How long people remain infectious
  • How easily the virus transmits between two people in contact

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Low is pursuing a PhD in infectious disease modelling at the University of Cape Town. Geffen is the director of the Centre for Science and Technology Mass Communication at Stellenbosch University

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