High SARS-CoV-2 seroprevalence in Lagos, Nigeria with robust antibody and cellular immune responses

Abstract

Background: Early evidence suggested that the impact of the COVID-19 pandemic was less severe in Africa compared to other parts of the world. However, more recent studies indicate higher SARS-CoV-2 infection and COVID-19 mortality rates on the continent than previously documented. Research is needed to better understand SARS-CoV-2 infection and immunity in Africa.

Methods: In early 2021, we studied the immune responses in healthcare workers (HCWs) at Lagos University Teaching Hospital (n = 134) and Oxford-AstraZeneca COVID-19 vaccine recipients from the general population (n = 116) across five local government areas (LGAs) in Lagos State, Nigeria. Western blots were used to simultaneously detect SARS-CoV-2 spike and nucleocapsid (N) antibodies (n = 250), and stimulation of peripheral blood mononuclear cells with N followed by an IFN-γ ELISA was used to examine T cell responses (n = 114).

Results: Antibody data demonstrated high SARS-CoV-2 seroprevalence of 72·4% (97/134) in HCWs and 60·3% (70/116) in the general population. Antibodies directed to only SARS-CoV-2 N, suggesting pre-existing coronavirus immunity, were seen in 9·7% (13/134) of HCWs and 15·5% (18/116) of the general population. T cell responses against SARS-CoV-2 N (n = 114) were robust in detecting exposure to the virus, demonstrating 87·5% sensitivity and 92·9% specificity in a subset of control samples tested. T cell responses against SARS-CoV-2 N were also observed in 83.3% of individuals with N-only antibodies, further suggesting that prior non-SARS-CoV-2 coronavirus infection may provide cellular immunity to SARS-CoV-2.

Conclusions: These results have important implications for understanding the paradoxically high SARS-CoV-2 infection with low mortality rate in Africa and supports the need to better understand the implications of SARS-CoV-2 cellular immunity.

Keywords: Africa; Antibody; COVID-19; Healthcare workers; Nigeria; SARS CoV-2; T-cell; Vaccine.

Fig. 1

Evolution of SARS-CoV-2 spike (S) in individuals in the general population post-vaccination. Sera sequentially collected from vaccine recipients in the general population were subjected to Western blot analysis. The post-vaccination evolution of SARS-CoV-2 S antibodies for each individual with baseline antibodies to A) SARS-CoV-2 S + N, B) S-only, C) N-only, or D) who were seronegative (red lines represent individuals who never developed S antibodies even after two vaccine doses) determined by image analysis where the S antibody signal was calculated and plotted as a % of control. The x-axis corresponds to number of days post-vaccination. The y-axis corresponds to background subtracted SARS-CoV-2 S signal normalized to the control line for each Western blot. Dashed line, cutoff. E) Representative image of Western blots for groups of individuals, including loading controls using COVID-19 positive and negative serum.

Fig. 2

Production of SARS-CoV-2 spike (S) in individuals in the general population post-vaccination. Sera sequentially collected from individuals in the general population were subjected to Western blot analysis. The level of antibody production was determined by subtracting the mean SARS-CoV-2 S antibody signal between baseline and 7-days post-vaccination, 7- and 14-days post-vaccination, and 14- and 84-days post-vaccination. The S signals from each time period were then summed and plotted as a% of total in a stacked format.

Fig. 3

T cell responses to SARS-CoV-2 nucleocapsid (N) in healthcare workers (HCWs) and individuals in the general populations. Whole blood samples were stimulated with SARS-CoV-2 N, then supernatants were processed via an IFN-γ enzyme-linked immunosorbent assay for A) healthcare workers and B) individuals in the general population who had antibodies to SARS-CoV-2 S + N, N-only, or were seronegative. Responses are expressed as an IU/mL. Dashed line, assay kit cutoff.