FIG 1.

Vaccination and previous infection induce robust serum antibody responses. Serum samples were collected from unvaccinated animals (n = 4), DTaP-vaccinated animals (n = 3), convalescent animals (n = 3), and animals vaccinated with DTwP (Triple Antigen, DT-COQ, or Quinvaxem; n = 2 per group) 1 week prior to challenge. Antibody responses to the four vaccine antigens, PT (A), FHA (B), PRN (C), FIM (D), and to heat-killed B. pertussis (E) were measured by enzyme-linked immunosorbent assay (ELISA). International units (IU) or relative units (RU) in each sample were determined by comparing the responses to the WHO international standard pertussis antiserum on each plate. For each group, the mean response is presented with error bars representing the standard error (SE).