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Support from Wits study for high seroprevalence in SA

In some part of Gauteng, up to 43% of the population already has COVID-19 antibodies, according to a study by Wits University vaccinologist Prof Shabir Madhi, writes MedicalBrief. The finding supports the conclusions of recent serosurveys by the National Institute of Communicable Diseases and the SA National Blood Service.

The SANBS study, conducted in January 2021, concluded that than half of South Africans probably have already been infected with SARS-CoV-2. The NICD survey, conducted in three communities across SA, found a seroprevalence of 41%.

Madhi's study is still to be published.

Madhi told the Sunday Times that a large serosurvey he headed in Gauteng showed that in some subdistricts, in Tshwane, seroprevalence was as low as 9%, whereas in others, in parts of Johannesburg, it was as high as 43%. This was the first survey done at general population level and provided estimates for all 26 subdistricts in the province.

The sample for the research, which was started in October when the first wave had subsided, included just under 6,000 people.The average seroprevalence for the whole province was extrapolated to be 19% but, said Madhi, if it is estimated from the study that 2.9-million in the province have antibodies, "one can multiply this by two" because of results on waning antibodies.

For Tshwane, it was estimated 13% of people have antibodies, whereas in Johannesburg the estimate was 25%. The serosurvey has since also been undertaken in the North West and the data is being analysed.

According to the South African Covid-19 Modelling Consortium, different studies done to date on seroprevalence "arrived at conflicting estimates" but "across months, a clear upward trend is discernible, with most estimates from January or February 2021 arriving at values of 30% to 40% seroprevalence".

In a study known as HUTS (Healthcare Utilisation and Seroprevalence), surveys were conducted in households in three communities – Pietermaritzburg, Mitchells Plain and Klerksdorp. Dr Nicole Wolter from the NICD told the Sunday Times that their serosurvey, showed "overall seroprevalence to be 41%".

We don't yet know how long antibodies last or how well they cross-protect against new variants of the virus, said Wolter, but there is "some indication" the severity of infection might be reduced.

Also under way is a very large Covid-19 study that marries behavioural research with biomedical research. The Human Sciences Research Council (HSRC) and partner organisations are conducting interviews and serosurveys in all provinces and across 400 communities.


Full report (Restricted access)


Prof Madhi's charts reproduced in a Gauteng Government Twitter thread (Study not yet published)


See also from MedicalBrief's archives:


‘Most South Africans have had COVID-19′ — National Blood Service study

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