Abstract
OBJECTIVES: To investigate the factors influencing SARS-CoV-2 IgG antibody levels and protection in a population that has experienced both vaccination and COVID-19 infections, predominantly caused by the Omicron BA.5.2 and BF.7 variants. METHODS: Anti-SARS-CoV-2 IgG antibody levels were measured using chemiluminescent microparticle immunoassay (CMIA). Multivariate regression analyses assessed factors influencing antibody levels, and decision tree models predicted variable priorities. RESULTS: Among the 3494 participants, the median (IQR) anti-SARS-CoV-2 IgG level was 396.53 (280.51-471.03) AU/mL, with a seropositive rate of 97.28%. Multivariate analysis revealed that vaccination status, infection status, residence county, occupation, and vaccination interval were significantly associated with antibody concentration. The decision tree model indicated that vaccination had a greater effect on antibody concentration than infection, while infection had a stronger impact on seropositivity. The Breakthrough Infection group had the highest antibody concentration compared with other groups. CONCLUSIONS: Vaccination and infection were identified as the primary determinants of SARS-CoV-2 IgG antibody levels, with hybrid immunity significantly enhancing antibody responses. New evaluation methods or revised detection thresholds were needed to better assess population immunity.