New research by the South African National Blood Service (SANBS) and other researchers have revealed a high number of South Africans have SARS-CoV-2 antibodies.
This research was conducted because of the lack of information about the true number of COVID-19 infections and people with antibodies in South Africa.
Population-level estimates of the prevalence of SARS-CoV-2 antibody positivity (seroprevalence) is a crucial epidemiological indicator for tracking the COVID-19 epidemic.
To help with community-level seroprevalence estimations, the SANBS joined forces with researchers to launch a nationally representative survey of blood donors.
The aim of the survey is to offer a cost-effective surveillance method with validity for community-level seroprevalence estimation.
To gather the needed information, blood donations collected on predefined days in January were tested for SARS-CoV-2 antibodies.
Using standard methods, the prevalence of antibodies was done by province, age, and race.
Testing was performed on blood from 4,858 donors in the Eastern Cape, Free State, KwaZulu Natal, and Northern Cape.
The researchers found a high prevalence of antibodies in their sample – 63% in the Eastern Cape, 52% in KwaZulu Natal, 46% in the Free State, and 32% in the Northern Cape.
Despite its limitations, it seems plausible that these estimates are reasonably generalisable to actual population-level anti-SARS-CoV-2 seroprevalence, but should be further verified.
The researchers noted that the high seroprevalence does not guarantee population-level immunity against new outbreaks – probably due to viral evolution and waning of antibody neutralization.
It was further discovered that the prevalence of antibodies varied substantially across race groups and between provinces.
The seroprevalence among black donors was consistently several times higher than among white donors, and the other main population groups – coloured and Asian.
There was no clear evidence that seroprevalence among donors varies by age.
The study also demonstrated substantial differences in the dissemination of SARS-CoV-2 infection between different race groups.
The differences are most likely explained by historically based differences in socioeconomic status and housing conditions.
The chart below shows the estimated prevalence of SARS-CoV-2 antibodies, expressed as a fraction between 0 (0%) and 1 (100%), for four South African provinces (EC=Eastern Cape, NC=Northern Cape, FS=Free State, ZN=KwaZulu Natal).
There is a differentiation by primary locally used racial designations (W)hite, (A)sian, (C)oloured and (B)lack, as well as a race-weighted (Tot)al provincial estimate.