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Covid-19: What we do and don’t know about second waves and herd immunity


Source: Alex Welte, Daily Maverick, 20 October 2020, photo credit: Shutterstock/LiveScience

There is much talk in South Africa about a ‘second wave’ of Covid-19. Spotlight places in perspective what we do and do not know about herd immunity and potential second waves.

As of the time of writing (mid-October 2020), there is much talk in South Africa about a “second wave” of Covid-19. In Europe, it is much more than talk, with Covid-19 diagnoses, hospital admissions, and deaths, not to mention “restrictions”, all on the rise.

Studies looking for antibodies in community surveys suggest that in most of Europe and North America a far smaller proportion of people have anti-Covid antibodies than what we see in developing world settings like India and Africa, including South Africa. This implies that there is currently more immunity here and people have been wondering out loud whether we have sufficient “herd immunity” to avoid our own “second wave”, and for how long.

There is a lot of jargon and technical discourse on such questions, framed in the language of mathematics and “dynamical modelling”. This discourse involves analysing how things work in “model worlds” where the rules are fully known and analysable – because we invent/declare the rules ourselves. Hopefully, we do this in a way that makes it possible to draw useful parallels between our model worlds and the real world. F

or the purposes of understanding how to brace for that possible second wave of Covid-19, this discourse is obscure, technically inaccessible to most people, and largely irrelevant. We can, however, unpack the key concepts in accessible ways that people will hopefully find useful.
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