Immunogenicity assessments
SEPARATION
Venous blood samples (5 mL) were obtained before vaccine administration (Day 0; baseline), and 28 days after vaccination (Day 28). It was then processed for serum separation on the same day. The blood sample was centrifuged at 1300g for 15 minutes at room temperature. The serum sample was collected and stored at −20 ⁰C and below prior to analysis. Concentrations of serum IgG antibody against PT