BackgroundGiven the low levels of COVID-19 vaccine coverage in Sub-Saharan Africa, despite high levels of natural SARS-CoV-2 exposures, strategies for extending the breadth and longevity of naturally acquired immunity are warranted. Designing such strategies will require a good understanding of natural immunity. MethodsWe used ELISA to measure whole-spike IgG and spike-receptor binding domain (RBD) total immunoglobulins (Igs) on 585 plasma samples collected longitudinally over five successive time points within six months of COVID-19 diagnosis in 309 COVID-19 patients. We measured antibody neutralizing potency against the wild-type (Wuhan) SARS-CoV-2 pseudo-virus in a subset of 51 patients over three successive time points. Binding and neutralizing antibody levels and potencies were then tested for correlations with COVID-19 severities, graded according to the National Institute of Health (NIH), USA criteria. ResultsRates of sero-conversion increased from Day 0 (day of PCR testing) to Day 180 (six months) (63.6% to 100 %) and (69.3 % to 97%) for anti-spike IgG and anti-spike-RBD binding Igs, respectively. Levels of these binding antibodies peaked at Day 28 (P<0.0001) and were subsequently maintained for six months without significant decay (p>0.99). Similarly, antibody neutralizing potencies peaked at Day 28 (p<0.0001) but had decreased by three-folds, six months after COVID-19 diagnosis (p<0.0001). Binding antibodies levels were highly correlated with neutralizing antibody potencies at all the time points analyzed (r>0.6, P<0.0001). Levels and potencies of binding and neutralizing antibodies increased with disease severity. ConclusionMost COVID-19 patients from Sub-Saharan Africa generate SARS-CoV-2 specific binding antibodies that remain stable during the first six months of infection. Although antibody binding levels and neutralizing potencies were directly correlated, the respective neutralizing antibodies decayed three-fold by the sixth month of COVID-19 diagnosis suggesting that they are short-lived, consistent with what has been observed elsewhere. Thus, just like for other populations, regular vaccination boosters will be required to broaden and sustain the high levels of predominantly naturally acquired anti-SARS-CoV-2 neutralizing antibodies.
Seychelles, an archipelago of 155 islands in the Indian Ocean, had confirmed 24,788 cases of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) by the 31st December 2021. The first SARS-CoV-2 cases in Seychelles were reported on the 14th of March 2020, but cases remained low until January 2021, when a surge of SARS-CoV-2 cases was observed on the islands. Here, we investigated the potential drivers of the surge by genomic analysis 1,056 SARS-CoV-2 positive samples collected in Seychelles between 14th March 2020 and 31st December 2021. The Seychelles genomes were classified into 32 Pango lineages, 1,042 of which fell within four variants of concern i.e., Alpha, Beta, Delta and Omicron. Sporadic cases of SARS-CoV-2 detected in Seychelles in 2020 were mainly of lineage B.1 (European origin) but this lineage was rapidly replaced by Beta variant starting January 2021, and which was also subsequently replaced by the Delta variant in May 2021 that dominated till November 2021 when Omicron cases were identified. Using ancestral state reconstruction approach, we estimated at least 78 independent SARS-CoV-2 introduction events into Seychelles during the study period. Majority of viral introductions into Seychelles occurred in 2021, despite substantial COVID-19 restrictions in place during this period. We conclude that the surge of SARS-CoV-2 cases in Seychelles in January 2021 was primarily due to the introduction of more transmissible SARS-CoV-2 variants into the islands.
