Background: In Australia, following the introduction of serogroup C meningococcal (MenC) conjugate vaccine for toddlers and catch-up immunization through adolescence, MenC disease incidence plummeted and remains low. However, individual protection following MenC conjugate vaccination, particularly in young children, may be short-lived. We investigated the persistence of MenC serum bactericidal antibody (SBA) titers in adolescents, more than 7 years after a single "catch-up" dose of MenC conjugate vaccine. We also investigated their exposure and susceptibility to meningococcal serogroups A, W and Y.
Methods: MenC SBA titers and Men A, C, W and Y IgG geometric mean concentration were measured in 240 healthy 11- to 16-year-old adolescents. The correlate of protection was an rSBA titer of ≥8.
Results: An rSBA≥8 was observed in 105 [44% (95% confidence interval {CI}, 37-50%)] of 240 adolescents (mean age, 13.2 years, mean interval since MenC immunization, 8.2 years). The proportion with an rSBA≥8, geometric mean rSBA titer and geometric mean IgG concentration increased with age, from 22% to 75%, 3.7 to 33.4 and 0.13 to 0.52 μg/mL, in participants who received MenC vaccine at mean age 2.8 to 7.5 years, respectively. Natural acquired antibody to Men A, W and Y was low with IgG geometric mean concentrations of 1.26, 0.38 and 0.47 μg/mL, respectively.
Conclusions: More than half of Australian adolescents have inadequate serological protection against MenC disease and low natural immunity to MenA, W and Y.