Hybrid immunity and host factors: implications on serostatus induced by COVID-19 vaccines

Introduction: Monitoring the humoral immune response following SARS-CoV-2 vaccination is crucial to understanding long-term protection, especially in the context of hybrid immunity (HI). This study aimed to evaluate anti-S IgG antibody levels in adults with and without prior COVID-19 infection and explore associated host-related factors. Methods: A cross-sectional study was conducted in 102 adults from Colombia, grouped by infection history: Group A (with prior COVID-19) and Group B (without prior COVID-19). Anti-S IgG levels were quantified using chemiluminescent immunoassay. Sociodemographic, clinical, and vaccination data were collected via survey. Statistical comparisons were performed using t-tests, Mann–Whitney U tests, and linear regression analysis. Results: All participants exhibited seropositivity (100%) for anti-S IgG, with high titers persisting up to 23 months post-booster. No significant differences in antibody concentrations were found between groups (p = 0.830). Variables such as sex, age, comorbidities, and type of vaccine did not significantly influence antibody levels. A moderate, significant correlation was found between the number of booster doses and antibody titers in Group A (ρ = 0.453; p = 0.001), but not in Group B. Regression analysis predicted progressively higher titers with additional booster doses. Conclusions: Robust humoral responses were observed regardless of prior infection, indicating effective vaccine-induced immunity in this population. The number of booster doses was a key factor associated with higher antibody titers, particularly in individuals with hybrid immunity. These findings support the value of continued booster campaigns and underline the need for further research into functional immunity.