Prevalence of anti-SARS-CoV-2 antibodies among blood donors in South Africa during the period January-May 2021

Abstract

Background: Population-level estimates of the prevalence of anti-SARS-CoV-2 antibody positivity (seroprevalence) are crucial epidemiological indicators 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 nationwide surveillance of blood donors. Methods: Leveraging existing arrangements, SANBS human research ethics committee permission was obtained to test blood donations collected on predefined days (in January and May 2021) for anti-SARS-CoV-2 antibodies, using the Roche Elecsys Anti-SARS-CoV-2 assay on the cobas e411 and e801 platforms currently available in the blood services’ donation testing laboratories. Using standard methods, prevalence analysis was done by province, age, time, sex and race. Results: We report on data from 16762 donations. Prevalence varied substantially across race groups and between provinces, with seroprevalence among Black donors consistently several times higher than among White donors, with the other main population groups (Coloured and Asian) not well represented in all provinces. There is no clear evidence that seroprevalence among donors varies by age or sex. The weighted national estimate of prevalence (in the core age range 15-69 years) is 47.4% (95% CI 46.2-48.6). From January to May, we noted a slight but statistically insignificant increase in seroprevalence in those provinces (Gauteng and Free State) where sufficient data were available to make such an estimate. Conclusions: Our study demonstrates substantial differences in dissemination of SARS-CoV-2 infection between different race groups and provinces, in patterns consistent with known differences in historically entrenched socio-economic status and housing conditions. As has been seen in other contexts, even such high seroprevalence does not guarantee population-level immunity against new outbreaks, as evidenced by a substantial third wave that has emerged almost contemporaneously with the end of sampling in this study. The relative importance of various contributions to this resurgence (notably viral evolution, waning of antibody neutralization efficacy, and infection control fatigue) are unclear. Despite its limitations, notably a ‘healthy donor’ effect and the possible waning of detectable antibodies over the time scale of the COVID-19 pandemic, it seems plausible that these estimates are reasonably generalisable to actual population level antiSARS-CoV-2 seroprevalence. The interpretation of occasional seroprevalence surveys as a proxy for total attack rates, over the ever-lengthening pandemic time scale is likely to become ever more complex. More frequent sampling, including linked repeat observations of frequent donors, could substantially improve the utility of blood donor surveillance.

Increased risk of SARS-CoV-2 reinfection associated with emergence of Omicron in South Africa

“…The primary limitation of this study is that changes in testing practices, health-seeking behavior, or access to care have not been accounted for in these analyses. Estimates based on serological data from blood donors suggest substantial geographic variability in detection rates ( 19 ), which may contribute to the observed differences in reinfection patterns by province (Supplementary Figure S1). Detection rates likely also vary through time and by other factors affecting access to testing, which may include occupation, age, and socioeconomic status.…”

Estimates of prevalence of anti-SARS-CoV-2 antibodies among blood donors in eight provinces of South Africa in November 2021

“…Anticipating that a fourth wave late in 2021 was inevitable (though there was no knowledge of the omicron variant at the time of planning), 3395 specimens were randomly collected from consenting donors from all provinces except the Western Cape (which has its own separate blood service) presenting to donate blood to the South African National Blood Service (SANBS) from 8 to 12 November 2021. This was carried out in accordance with previous arrangements and practices underlying our previous rounds of sampling [1,2], as approved by the SANBS Human Research Ethics Committee (HREC).…”

“…We have previously published estimates of the prevalence of anti-SARS-CoV-2 antibodies among blood donors in South Africa, based on specimens collected from January to May 2021 [1,2], as well as estimates of fatality rates, based on these prevalence estimates and publicly available excess deaths estimates [3].…”

Biological Properties of SARS-CoV-2 Variants: Epidemiological Impact and Clinical Consequences

“…Early estimates suggested that the Beta variant had a transmission rate of 23-50% compared to ancestral lineages [159]. Seroprevalence estimates from blood donor surveys ranged from 32% to 62% across South Africa's nine provinces, with a weighted national estimate of 47% following the second wave peak in January 2021 [160]. A report on SARS-CoV-2 variant transmission in Switzerland estimated a 50% increase in transmissibility [103].…”

“…When compared to White people in the COVID-19 study, those of the Black race and those who live in impoverished neighborhoods were identified as population categories that may be more vulnerable to the unfavorable influence of PM 2.5 on hospitalization risk [368]. In a study conducted in South Africa by Vermeulen et al (2021) (data from 16,762 test blood donations received between January and May 2021 for anti-SARS-CoV-2 antibodies) seroprevalence in Black donors was consistently several times higher than in White donors, with the other major population groups (Colored and Asian) not well represented in any regions [160].…”