Immune response to SARS-CoV-2 vaccination in adults from Cali, Colombia: a 2022 experience

Introduction: Immunization is a protective measure against SARS-CoV-2. This study assessed IgG anti-S antibodies levels and their association with clinical, demographic and vaccination-related factors in adults from Cali, Colombia (2021-2022). Objective: To analyze factors associated with binding antibodies levels in adults with a complete SARS-CoV-2 vaccination schedule in a middle-income country city. Methods: A cross-sectional study was conducted between December 2021 and February 2022 in Cali, Colombia. Eligible adults were identified from a local health database and recruited through random sampling and media outreach. A total of 394 participants were included. Data on demographics, vaccination, and COVID-19 history were collected via interviews and verified with official records. IgG antibodies against the SARS-CoV-2 Spike protein were measured using a standardized ELISA, and results were expressed in BAU/mL following WHO calibration. A cut-off of 1,000 BAU/mL defined high antibody response. Statistical analyses were performed with GraphPad Prism and Stata 14, using logistic regression to explore associations. The study was approved by the Universidad Libre Ethics Committee, and informed consent was obtained from all participants. Results: Seventy percent of participants showed specific antibodies titers ≥1000 BAU/mL (binding antibodies units). Associations were observed with: a) mRNA vaccines (aOR: 2.40; 95% CI: 0.99–5.84; p = 0.053); b) heterologous vaccination schemes (aOR: 2.39; 95% CI: 1.14–5.02; p < 0.021); and c) ≥21 days since the booster dose (aOR: 2.62; 95% CI: 1.29–5.30; p < 0.007). Women showed a stronger response with heterologous schemes (aOR: 3.27; 95% CI: 0.99–5.84; p = 0.008) and mRNA vaccines (aOR: 3.03; 95% CI: 0.99–5.84; p = 0.048). Among men, antibodies levels were higher when measured ≥21 days after the booster dose (aOR: 2.62; 95% CI: 1.29–5.30; p < 0.007). Conclusions: mRNA vaccines, heterologous vaccination schedules, and a longer interval since the booster dose were associated with higher anti-S IgG antibodies levels. These findings, relevant to middle-income countries, support the adaptation of vaccination strategies to specific population characteristics.