Neisseria meningitidis is a leading cause of bacterial meningitis worldwide. Most cases in developed countries are caused by endemic disease. The incidence is around 1-2 per 100 000,1 2 3 with rates among infants as high as 20 per 100 000.2 Children younger than 2 years have the highest incidence of meningococcal disease, with a second peak between 15 and 24 years. Most cases are caused by serogroups A, B, C, W-135, and Y. Serogroups C and B predominate in temperate countries.1 2 3

In the accompanying study, Snape and colleagues evaluate the persistence of serum bactericidal antibody against meningococcal serogroup C in a large cohort of adolescents originally immunised with serogroup C meningococcal conjugate vaccines at 6-15 years of age.4 These vaccines, now used in many countries, were licensed on the basis of immunogenicity rather than clinical efficacy.5 Despite the high public profile of meningococcal disease, it is relatively rare, which makes traditional efficacy studies …