Detection of EBOV antibodies, Lagos, Nigeria.

<p>(A) Sera samples from 3 EVD survivors, 10 documented EVD contacts, and 6 control HCWs were subjected to LFn-EBOV-GP1 and LFn-EBOV-sGP Western blot analysis. +, positive control. Molecular size marker units are kDa. EVD, Ebola virus disease. Control HCWs, control healthcare workers.</p

Detection of EBOV antibodies, 1976 Democratic Republic of Congo.

<p>(A) Representative image of reactive LFn-EBOV-GP and LFn-EBOV-sGP Western blot analysis in 9 sera collected in surrounding areas of the 1976 Ebola virus outbreak in the Democratic Republic of Congo. +, positive control. Molecular size marker units are kDa. EVD, Ebola virus disease.</p

qRT-PCR, antigen ELISA, and serology results, Lagos, Nigeria.

<p>qRT-PCR, antigen ELISA, and serology results, Lagos, Nigeria.</p

Serology results, 1976 Democratic Republic of Congo.

<p>Serology results, 1976 Democratic Republic of Congo.</p

Ex vivo CD8+ and CD4+ cellular reactivity to EBOV LFn fusion proteins, Lagos, Nigeria.

<p>CD8+ and CD4+ cells from the EVD survivors and documented EVD contacts were treated with the LFn-EBOV fusion proteins and the IFN-γ+ and TNF-α+ responses were detected by LFn ELISPOT ex vivo experiments. Individual and mean CD8+ IFN-γ+ (A) and TNF-α+ (B) and CD4+ IFN-γ+ (C) and TNF-α+ (D) responses are shown. Dotted lines represent the cut-off value. Control HCWs, control healthcare workers. *, p<0.05.</p

Cellular immune responses, Lagos, Nigeria.

<p>PBMC samples from the EVD survivors, documented EVD contacts, and control HCWs were treated with the LFn-EBOV fusion proteins and the IFN-γ+ and TNF-α+ cellular responses were detected by LFn ELISPOT ex vivo experiments. Representative image of IFN-γ (A) and TNF-α (B) cellular responses when stimulated with the LFn-Ebola virus fusion proteins. NP, LFn-EBOV-NP. VP40, LFn-EBOV-VP40. GP1, LFn-EBOV-GP1. LFn, negative control. PHA, phytohemaglutanin, positive control.</p

Ex vivo cellular reactivity to EBOV LFn fusion proteins, Lagos, Nigeria.

<p>PBMC samples from the EVD survivors and documented EVD contacts were treated with the LFn-EBOV fusion proteins and the IFN-γ+ and TNF-α+ cellular responses were detected by LFn ELISPOT ex vivo experiments. Average magnitude of convalescent IFN-γ (A) and TNF-α (B) responses are shown. Dotted lines represent the cut-off value. Control HCWs, control healthcare workers. *, p < 0.05.</p

Ex vivo ELISPOT results using the LFn-EBOV fusion proteins, Lagos, Nigeria.

<p>Ex vivo ELISPOT results using the LFn-EBOV fusion proteins, Lagos, Nigeria.</p

Table_1_Immunological insights into COVID-19 in Southern Nigeria.docx

IntroductionOne of the unexpected outcomes of the COVID-19 pandemic was the relatively low levels of morbidity and mortality in Africa compared to the rest of the world. Nigeria, Africa's most populous nation, accounted for less than 0.01% of the global COVID-19 fatalities. The factors responsible for Nigeria's relatively low loss of life due to COVID-19 are unknown. Also, the correlates of protective immunity to SARS-CoV-2 and the impact of pre-existing immunity on the outcome of the COVID-19 pandemic in Africa are yet to be elucidated. Here, we evaluated the natural and vaccine-induced immune responses from vaccinated, non-vaccinated and convalescent individuals in Southern Nigeria throughout the three waves of the COVID-19 pandemic in Nigeria. We also examined the pre-existing immune responses to SARS-CoV-2 from samples collected prior to the COVID-19 pandemic.MethodsWe used spike RBD and N- IgG antibody ELISA to measure binding antibody responses, SARS-CoV-2 pseudotype assay protocol expressing the spike protein of different variants (D614G, Delta, Beta, Omicron BA1) to measure neutralizing antibody responses and nucleoprotein (N) and spike (S1, S2) direct ex vivo interferon gamma (IFNγ) T cell ELISpot to measure T cell responses. ResultOur study demonstrated a similar magnitude of both binding (N-IgG (74% and 62%), S-RBD IgG (70% and 53%) and neutralizing (D614G (49% and 29%), Delta (56% and 47%), Beta (48% and 24%), Omicron BA1 (41% and 21%)) antibody responses from symptomatic and asymptomatic survivors in Nigeria. A similar magnitude was also seen among vaccinated participants. Interestingly, we revealed the presence of preexisting binding antibodies (N-IgG (60%) and S-RBD IgG (44%)) but no neutralizing antibodies from samples collected prior to the pandemic. DiscussionThese findings revealed that both vaccinated, non-vaccinated and convalescent individuals in Southern Nigeria make similar magnitude of both binding and cross-reactive neutralizing antibody responses. It supported the presence of preexisting binding antibody responses among some Nigerians prior to the COVID-19 pandemic. Lastly, hybrid immunity and heterologous vaccine boosting induced the strongest binding and broadly neutralizing antibody responses compared to vaccine or infection-acquired immunity alone.</p