Seroprevalence of meningococcal serogroup C bactericidal antibody in England and Wales in the pre-vaccination era.

Sera from an age-stratified sample of 1689 individuals, submitted to the PHLS Seroepidemiology Unit between 1996 and 1999 were tested for serum bactericidal antibodies to serogroup C meningococci. Titres decreased during infancy, presumably as maternal antibody waned, and increased in older teenagers, the peak age of meningococcal carriage. The prevalence of antibody titres greater than or equal to 8 was highest in adults, with an average of 25% of adults 25 years old or above with titres above this putative protective level. In the absence of vaccination, antibody may be generated from periods of carriage of serogroup C meningococci, from other meningococcal strains sharing non-capsular antigens, and other cross-reactive organisms. The inverse relationship between disease incidence and the prevalence of 'protective' antibody titres as described by Goldschneider et al. appears more consistent with a titre of > or =8 rather than > or =128, although the proportions 'protected' are much lower here than in Goldschneider's study. This study provides baseline antibody levels which will facilitate the evaluation of the meningococcal serogroup C conjugate vaccination programme.