SARS-CoV-2 Seroprevalence and Antibody Dynamics in The Gambia During the Transition from Pandemic to Endemic Circulation - 2022 and 2023.

OBJECTIVES

To understand population-level seroprevalence once SARS-CoV-2 becomes endemic.

METHODS

We conducted two cross-sectional-sero-surveys (CSS) in three Health and Demographic Surveillance Systems (HDSS) in The Gambia: Farafenni, Basse and Kiang West. Dried blood spots were collected from 3909 participants in CSS1_2022 and 3991 in CSS2_2023, aged ≥1-year. SARS-CoV-2-spike (S-IgG) and nucleocapsid (NCP-IgG) proteins were measured by ELISA in both CSSs, while antibodies to SARS-CoV-2 variants and other respiratory viruses were quantified by multiplex-Luminex in CSS2_2023. Another CSS was conducted in Kiang West (KW survey) 3-months after CSS1_2022 to assess antibody dynamics. Statistical analysis was done using Stata/SE19.5.

RESULTS

S-IgG seroprevalence increased between CSS1_2022 and CSS2_2023 [88.1% 95%CI (86.3, 89.6) vs. 93.1% (92.0, 94.0), p<0.0001], whereas NCP-IgG seroprevalence declined [72.7% (70.7, 74.7) vs 61.7% (59.3, 63.9), p<0.0001]. S-IgG seroprevalence was higher in vaccinated vs. unvaccinated individuals [CSS1_2022 [aOR = 3.11(1.85, 5.23)] and CSS2_2023 [2.01(1.18, 3.42)]. SARS-CoV-2 variants seroprevalence ranged between 50%-80%, while seroprevalence to other respiratory viruses was more heterogeneous. In the KW survey, S-IgG seroprevalence remained stable compared with CSS1_2022: 89.2% (85.3, 92.3), while NCP-IgG seroprevalence dropped from 73.1% (68.5, 77.3) to 61.2% (53.6, 68.4).

CONCLUSION

By 2022-2023, SARS-CoV-2 exposure in The Gambia was nearly universal. Still, COVID-19 vaccinated individuals showed highest seroprevalence.