Serum immunoglobulin G and mucosal immunoglobulin A antibodies from prepandemic samples collected in Kilifi, Kenya, neutralize SARS-CoV-2 in vitro

Rethinking the evidence on COVID-19 in Africa

The COVID-19 pandemic was predicted to cause substantial mortality in Africa. However, some countries in Africa had a striking absence of overwhelmed hospitals and low reported mortality. The marked contrast with the overwhelmed hospitals and high mortality seen in Europe and other high-income settings was regarded as puzzling and a paradox. In this Review, we reflect on possible explanations for the paradox with particular reference to observations made on the ground in Kenya. The evidence is inconsistent with reduced viral transmission or poor surveillance as primary explanations for the discrepancy. Population age structure is an important but incomplete explanation of the epidemiology. Due to the high prevalence of asymptomatic infection, low mortality, and evidence of reduced inflammatory responses, we hypothesise that some populations in Africa might have reduced susceptibility to symptomatic COVID-19. The reduced inflammatory responses might result from immunoregulation or cross-reactive, pre-pandemic cellular immunity, although the evidence is not definitive. Local data are essential to develop public health policies that align with the reality on the ground rather than external perceptions.

Evaluation of population immunity against SARS-CoV-2 variants, EG.5.1, FY.4, BA.2.86, JN.1, JN.1.4, and KP.3.1.1 using samples from two health demographic surveillance systems in Kenya

Increased immune evasion by emerging and highly mutated SARS-CoV-2 variants is a key challenge to the control of COVID-19. The majority of these mutations mainly target the spike protein, allowing the new variants to escape the immunity previously raised by vaccination and/or infection by earlier variants of SARS-CoV-2. In this study, we investigated the neutralizing capacity of antibodies against emerging variants of interest circulating between May 2023 and October 2024 using sera from representative samples of the Kenyan population. From our genomics data, we identified the most prevalent Kenyan and global variants and performed pseudoviruses neutralization assays with the most recent SARS-CoV-2 variants. Our data show that antibodies from individuals in the general population in Kenya were less effective against the recent prevalent SARS-CoV-2 omicron variants (i.e. EG.5.1, FY.4, BA.2.86, JN.1, JN.1.4, and KP.3.1.1) compared to the ancestral wildtype strain. Although there was increased neutralization following multiple doses of vaccine, antibodies from > 40% of the vaccinated individuals did not neutralize the omicron variants, suggesting that individuals were susceptible to infection by these variants.

The single-dose Janssen Ad26.COV2.S COVID-19 vaccine elicited robust and persistent anti-spike IgG antibody responses in a 12-month Ugandan cohort

Introduction

The study investigation examined the immune response to the Janssen Ad26.COV2.S COVID-19 vaccine within a Ugandan cohort, specifically targeting antibodies directed against spike (S) and nucleocapsid (N) proteins. We aimed to examine the durability and robustness of the induced antibody response while also assessing occurrences of breakthrough infections and previous anti-Spike seropositivity to SARS-CoV-2.

Methods

The study included 319 specimens collected over 12 months from 60 vaccinees aged 18 to 64. Binding antibodies were quantified using a validated ELISA method to measure SARS-CoV-2-specific IgG, IgM, and IgA levels against the S and N proteins.

Results

The results showed that baseline seropositivity for S-IgG was high at 67%, increasing to 98% by day 14 and consistently stayed above 95% for up to 12 months. However, S-IgM responses remained suboptimal. A raised S-IgA seropositivity rate was seen that doubled from 40% at baseline to 86% just two weeks following the initial vaccine dose, indicating sustained and robust peripheral immunity. An increase in N-IgG levels at nine months post-vaccination suggested breakthrough infections in eight cases. Baseline cross-reactivity influenced spike-directed antibody responses, with individuals harbouring S-IgG antibodies showing notably higher responses.

Discussion

Robust and long lasting vaccine and infection-induced immune responses were observed, with significant implications for regions where administering subsequent doses poses logistical challenges.

Prepandemic cross-reactive humoral immunity to SARS-CoV-2 in Africa: Systematic review and meta-analysis

OBJECTIVES

To assess the evidence on the presence of antibodies cross-reactive with SARS-CoV-2 antigens in prepandemic samples from African populations.

METHODS

We performed a systematic review and meta-analysis of studies evaluating prepandemic African samples using pre-set assay-specific thresholds for SARS-CoV-2 seropositivity.

RESULTS

In total, 26 articles with 156 datasets were eligible, including 3437 positives among 29,923 measurements (11.5%) with large between-dataset heterogeneity. Positivity was similar for anti-nucleocapsid (14%) and anti-spike antibodies (11%), higher for anti-spike1 (23%), and lower for anti-receptor-binding domain antibodies (7%). Positivity was similar, on average, for immunoglobulin M and immunoglobulin G. Positivity was seen prominently in countries where malaria transmission occurs throughout and in datasets enriched in malaria cases (14%, 95% confidence interval, 12-15% vs 2%, 95% confidence interval 1-2% in other datasets). Substantial SARS-CoV-2 reactivity was seen in high malaria burden with or without high dengue burden (14% and 12%, respectively), and not without high malaria burden (2% and 0%, respectively). Lower SARS-CoV-2 cross-reactivity was seen in settings of high HIV seroprevalence. More sparse individual-level data showed associations of higher SARS-CoV-2 cross-reactivity with Plasmodium parasitemia and lower SARS-CoV-2 cross-reactivity with HIV seropositivity.

CONCLUSION

Prepandemic samples from Africa show high levels of anti-SARS-CoV-2 seropositivity. At the country level, cross-reactivity tracks especially with malaria prevalence.

Prevalence of immunoglobulin G and M to SARS-CoV-2 and other human coronaviruses in The Democratic Republic of Congo, Sierra Leone, and Uganda: A longitudinal study

OBJECTIVES

We assessed the prevalence of immunoglobulin G (IgG) and IgM against four endemic human coronaviruses and two SARS-CoV-2 antigens among vaccinated and unvaccinated staff at health care centers in Uganda, Sierra Leone, and the Democratic Republic of Congo.

METHODS

The government health facility staff who had patient contact in Goma (Democratic Republic of Congo), Kambia District (Sierra Leone), and Masaka District (Uganda) were enrolled. Questionnaires and blood samples were collected at three time points over 4 months. Blood samples were analyzed with the Luminex MAGPIXⓇ.

RESULTS

Among unvaccinated participants, the prevalence of IgG/IgM antibodies against SARS-CoV-2 receptor-binding domain or nucleocapsid protein at enrollment was 70% in Goma (138 of 196), 89% in Kambia (112 of 126), and 89% in Masaka (190 of 213). The IgG responses against endemic human coronaviruses at baseline were not associated with SARS-CoV-2 sero-acquisition during follow-up. Among the vaccinated participants, those who had evidence of SARS-CoV-2 IgG/IgM at baseline tended to have higher IgG responses to vaccination than those who were SARS-CoV-2 seronegative at baseline, controlling for the time of sample collection since vaccination.

CONCLUSION

The high levels of natural immunity and hybrid immunity should be incorporated into both vaccination policies and prediction models of the impact of subsequent waves of infection in these settings.