TITLE:
Dynamics of Antibody Responses to COVID-19 Vaccination in Senegalese Adults: A Multicentre Longitudinal Study
AUTHORS:
Flore Biscotine N. Makoutchouang, Nalda Debsikréo, N’da Kouamé Nazaire Kouadio, Isaac Darko Otchere, Ndeye Dieynaba Diouf, Abdoulaye Leye Sarr, Mame Sokhna Gueye, Joséphine Khady Badiane, Ousmane Diouf, Aminata Mboup, Nafissatou Leye, Souleymane Mboup, Tandakha Ndiaye Dieye, Djibril Wade
KEYWORDS:
COVID-19, Vaccination, Humoral Response, Johnson & Johnson, Sinopharm, Kinetics, Adult Cohort, Senegal, Longitudinal Study
JOURNAL NAME:
Open Journal of Immunology,
Vol.16 No.1,
March
31,
2026
ABSTRACT: Background: The COVID-19 pandemic, caused by the SARS-CoV-2 virus, affected hundreds of millions of people worldwide and resulted in significant mortality. In Senegal, over 89,000 infections and nearly 2000 deaths were reported. The deployment of the Johnson & Johnson (adenoviral vector) and Sinopharm (inactivated virus) vaccines through the COVAX initiative and bilateral partnerships was crucial in mitigating the spread of the virus. However, little local data existed regarding their immunogenicity. This study aimed to evaluate the humoral immune response induced by the Johnson & Johnson and Sinopharm COVID-19 vaccines among Senegalese adults aged 18 years and older over a 12-month period. Methods: This longitudinal multicentre study was conducted between August 2022 and August 2023 with 375 adult volunteers. Plasma samples were collected and tested using the Q-Plex SARS-CoV-2 Human IgG (5-plex) kit to quantify antibodies targeting the S1, S2, and NP proteins of SARS-CoV-2. Follow-up visits were scheduled based on the vaccine received: Johnson & Johnson vaccine recipients had 7 time points (Day 0, Day 14, Day 28, Month 3, Month 6, Month 9, and Month 12), while Sinopharm vaccine recipients had 8 time points (Day 0, Day 14, Day 28(Day 0B), Day 14B, Day 28B, Month 6, Month 9, and Month 12). Analysis of antibody levels was stratified by vaccine type, age, sex, and period of sampling after vaccination. Results: Both vaccines elicited detectable antibody responses, albeit with disparate dynamics. Johnson & Johnson induced a stronger response (S1: 490.66, S2: 1068.12, NP: 161.45) in young adults aged 18 - 30 years, while Sinopharm showed a better initial response (S1: 868.61, S2: 1608.58, NP: 310.88) in older individuals (46 - 70 years). However, antibody levels declined progressively in both groups over time (from S1: 465.99, S2: 1003, NP: 157.98 to S1: 210.01, S2: 466.88, NP: 141.39 and from S1: 451.36, S2: 1075.51, NP: 207.39 to S1: 446.74, S2: 631.09, NP: 142.59). Notably, women demonstrated more persistent antibody responses than men. Strong associations were observed between antibody positivity and sociodemographic factors such as household size, occupation, and formal educational level. Conclusion: This study confirms the immunogenicity of both Johnson & Johnson and Sinopharm vaccines in the Senegalese population, with appreciable levels of antibody production that gradually wane over time, supporting the need for booster doses to sustain long-term immunity. Differences in antibody responses by age, sex, and vaccine type highlight the role of individual and contextual factors. These findings underscore the importance of tailoring vaccination strategies and serological monitoring to local realities.