Evolution of variants of concern of SARS-CoV-2 during three waves in Senegal

ABSTRACT

Introduction/ Background: In Senegal, SARS-CoV-2 incidence evolved with three successive epidemic waves. The first wave started on March 2020 with low virus variability whilst the second outbreak started in December was dominated by the Alpha variant. With the third taking place in June 2021, we investigated the involvement of other variants. Methods: During three waves of the pandemic, 163,788 nasopharyngeal swabs have been analysed at the Institut de Recherche en Santé, de Surveillance Epidémiologique et de Formations (IRESSEF). From those, 10,189 positive samples were screened with Seegene Real-time reverse-transcription polymerase chain reaction RT-PCR new variant. From the screened samples, 972 positives were sequenced and 10% of the negatives for detection of new variants. The ARTIC Network methodology with Oxford Nanopore Technologies (ONT) has been used for sequencing. Results: Our data have overall shown that the Senegalese strains are very similar to each other or closely related to other. During the first wave, the most common clade found was 19A (70.27%) and majority of the samples were of the B.1 (54.05) lineage. We noted more diversity during the second wave where clade 20B (40.82%) was more frequent, followed by clade 20A (28.91%), 20I (10.54%). At the level of lineages, we identified variants of interest as B.1.1.7 (10.54%), B.1.525 (6.12%), and B.1.617.2 (0.68%). In the third wave, we observed at the clade level with mainly 21D (47.69%) and 21A (20%). Impact SARS-CoV-2 diversity may affect the virus's properties, such as it spreads, disease severity, performance of vaccines, tools, or other public health and social measures. Therefore, such tracking of SARS-CoV-2 variants highlight the role some African institutes like IRESSEF surveillance capabilities through real-time sequencing of SARS-CoV-2 genomes in the local context. Conclusion: In Senegal, the SARS-CoV-2 pandemic has disrupted the organization of the health system. IRESSEF contributed to put in place strategies to respond effectively to the expectations of medical authorities by providing them with data on the strains circulating in Senegal at each moment of the epidemic.