Host Immune Responses to SARS-CoV-2 Vaccination in Northern Mexico: Structural Biology Insights and the Impact of Obesity

Understanding the molecular mechanisms underlying host immune responses to SARS-CoV-2 vaccination remains essential, particularly in populations with a high prevalence of obesity. In this cross-sectional study, we evaluated whether body mass index (BMI) is associated with vaccine-induced humoral immunity in a cohort from northeastern Mexico and discuss the findings within a structural immunology framework of spike antigenicity and antibody–epitope interactions. A total of 138 adults were recruited in Reynosa and Matamoros (June 2021–June 2022) and categorized as healthy weight, overweight, or obese according to BMI criteria. Serum anti-SARS-CoV-2 IgG was assessed using an ELISA-based assay, and differences across BMI groups were tested using the Kruskal–Wallis approach. Among all participants, 33.3% were classified as obese and 99.3% (137/138) were seropositive for anti-SARS-CoV-2 IgG. No significant differences in IgG levels were detected between BMI categories (p = 0.20). These results indicate that, in this Mexican cohort—sampled during a period of heterogeneous and often incomplete vaccination schedules—obesity was not associated with reduced detectable anti-SARS-CoV-2 IgG responses. Our findings support the need to integrate population-level serology with mechanistic studies that interrogate antibody quality (e.g., neutralization potency and epitope specificity) to better connect clinical determinants such as obesity with molecular correlates of protection.