Multicenter Assessment of SARS-CoV-2 Immunity in Vulnerable Populations in Senegal (April to August 2022)

Introduction: The COVID-19 pandemic due to SARS-CoV-2 has progressed slowly in Africa, despite the alarmist predictions that were made. Vulnerable people are considered at risk of developing severe and complicated forms once they are infected. Despite relatively low reported COVID-19 cases in Africa, limited data exist on immune responses among high-risk groups such as the elderly and those with comorbidities. Then, it is important to have data about epidemiological seroprevalence and asymptomatic carriage to understand their behaviour in the face of infection. Objectives: Screen for SARS-CoV-2 markers (genome and specific antibodies) in vulnerable people in three regions of Senegal (Thies, Saint-Louis and Ziguinchor) over a six-month period. Methodology: This was a multicenter study conducted in three regions of Senegal (in 3 sites: Saint Louis in the North, Thies in the center ouest et Ziguinchor in the South) among people over 65 years of age and/or with comorbidities in 2022. For each participant, after consent, SARS-CoV-2 genome detection was performed by RT-PCR and qualitative and quantitative anti-antibodies were performed using immunochromatography and chemiluminescence immunoassay tests. Results: 737 people with the described criteria for vulnerability to COVID-19 were enrolled. Their median age was 58 years and 26.7% (n = 197) of them were older than 65 years. The female-to-male ratio was 2.23. The main comorbidities were hypertension (26.18%), pregnancy (21.7%), diabetes mellitus (14.24%) and age > 65 years. Vaccination coverage was 38.34%, mostly by Sinopharm vaccine. RT-PCR was positive for 20 participants who had all received at least one dose of COVID-19 vaccine. IgG antibodies were found in an average of 73% of participants, and with some having antibody titers up to 40,000. Conclusion: This study highlights the significant presence of antibodies in a majority of vulnerable peoples, despite a low proportion of RT-PCR positivity. Vaccination appears playing an important role in immune response, but the persistence of antibodies and their long-term efficacy require continued monitoring. Then, it is importance to continue vaccination and epidemiological surveillance efforts to better protect vulnerable populations. So, the study provides baseline data essential for guiding vaccination policies and resource allocation in low- and middle-income countries.