Prevalence of anti-SARS-CoV-2 antibodies among blood donors in Northern Cape, KwaZulu-Natal, Eastern Cape, and Free State provinces of South Africa in January 2021.

Abstract

Background: Population-level estimates of prevalence of anti-SARS-CoV-2 antibody positivity (seroprevalence) is a crucial epidemiological indicator for tracking the Covid-19 epidemic. Such data are in short supply, both internationally and in South Africa. The South African blood services (the South African National Blood Service, SANBS and the Western Cape Blood Service, WCBS) are coordinating a nationally representative survey of blood donors, which it is hoped can become a cost-effective surveillance method with validity for community-level seroprevalence estimation.Methods: Leveraging existing arrangements, SANBS human research ethics committee permission was obtained to test blood donations collected on predefined days (7th, 10th ,12th ,15th ,20th ,23th and 25th January) for anti-SARS-CoV-2 antibodies, using the Roche Elecsys Anti-SARS-CoV-2 assay on the cobas e411 platform currently available in the blood services’ donation testing laboratories. Using standard methods, prevalence analysis was done by province, age and race, allowing age to be regarded as either a continuous or categorical variable. Testing was performed in the Eastern Cape (EC), Free State (FS), KwaZulu Natal (ZN) and Northern Cape (NC) provinces.Results: We report on data from 4858 donors - 1457 in EC; 463 in NC; 831 in FS and 2107 in ZN. Prevalence varied substantially across race groups and between provinces, with seroprevalence among Black donors consistently several times higher than among White donors, and the other main population groups (Coloured and Asian) not consistently represented in all provinces. There is no clear evidence that seroprevalence among donors varies by age. Weighted net estimates of prevalence (in the core age range 15-69) by province (compared with official clinically-confirmed COVID-19 case rates in mid-January 2021) are: EC-63%(2.8%), NC-32%(2.2%), FS-46%(2.4%), and ZN-52%(2.4%).Conclusions: Our study demonstrates substantial differences in dissemination of SARS-CoV-2 infection between different race groups, most likely explained by historically based differences in socio-economic status and housing conditions. As has been seen in other areas, even such high seroprevalence does not guarantee population-level immunity against new outbreaks – probably due to viral evolution and waning of antibody neutralization. Despite its limitations, notably a ‘healthy donor’ effect, it seems plausible that these estimates are reasonably generalisable to actual population level anti-SARS-CoV-2 seroprevalence, but should be further verified.

Rural prioritization may increase the impact of COVID-19 vaccines in Sub-Saharan Africa due to ongoing internal migration: A modeling study

“…A less contained, widespread outbreak was generated when transmission and migration rates were high (R 0 = 2.8 and migration = 200 000 dtpmi); cumulative incidence was 78% and 63% in urban and rural areas, respectively, and 68% ± 2% at the country level (Figure 2). This range of cumulative incidence was consistent with seroprevalence rates in SSA [10,11,12,13,14].…”

Temporal trends of SARS-CoV-2 seroprevalence during the first wave of the COVID-19 epidemic in Kenya

“…Nonetheless, they also show that the virus was widely transmitted during the first epidemic wave even though numbers of cases and deaths attributable to SARS-CoV-2 in Kenya were very low by comparison with similar settings in Europe and the Americas at similar seroprevalence 17,18 . This pattern of widespread SARS-CoV-2 transmission and higher cumulative exposure in general [19][20][21][22] and targeted populations (including blood donors) [23][24][25][26] compared to disproportionately lower COVID-19 case numbers and deaths has also been seen across epidemic waves in other parts of Africa. This disparity may be attributable to constraints on morbidity/ a Bayesian Multi-level Regression with Post-stratification (MRP) accounts for differences in the age and sex distribution of blood donors and regional differences in the numbers of samples collected over time.…”

Rapidly increasing SARS-CoV-2 seroprevalence and limited clinical disease in three Malian communities: a prospective cohort study

“…Using commercial point of care tests, community serosurveillance throughout 2020 has identified gradually increasing seroprevalence rates in West African countries, including 0.9% in Togo in April, 25.4% in Nigeria in June, and 25.1% in Côte d’Ivoire in October [7-9]. Similarly, surveys in other parts of the continent using laboratory-based single antigen ELISA have estimated seroprevalence rates of 4.3% in Kenyan blood donors in June 2020, 2.1% in households in Zambia in July, and up to 60% in blood donors in parts of South Africa in January 2021 [10-12]. These results suggest that SARS-CoV-2 is circulating throughout Africa, in some cases potentially at a subclinical level, and that there may be a largely unquantified community reservoir of transmission.…”