Prevalence of serum bactericidal antibody to serogroup C Neisseria meningitidis in England a decade after vaccine introduction

Abstract

Serogroup C meningococcal disease incidence and carriage declined rapidly in the United Kingdom after infant serogroup C conjugate vaccination was introduced in 1999, with catch-up vaccination for children under 18 years. Antibody levels and effectiveness waned quickly in children vaccinated at 2, 3, and 4 months of age. Therefore, in 2006, the current revised schedule of doses at 3, 4, and 12 months was introduced. This study assessed age-specific protection in 2009 compared with data from historical prevaccination and early postvaccination studies. Rabbit complement serum bactericidal antibody (SBA) was measured in anonymously banked serum samples collected in England in 2009 (n = 1,174), taking titers of ≥ 8 as protective. Age-stratified proportions of SBA titers that were ≥ 8 and geometric mean titers were compared. SBA titers varied markedly by birth cohort and time since vaccination. Overall, 35% of samples (95% confidence interval [CI], 33 to 38%) had titers that were ≥ 8. Only in cohorts eligible for catch-up vaccination did the majority of individuals have protective antibody levels. Antibody levels were higher in children eligible for vaccination at primary and secondary school ages, compared to those eligible below the age of 5 years. In those eligible for completed vaccination under the current schedule, protective levels were very modest and there was no evidence of superiority to cohorts that were eligible for the previous schedule. This supports a need for older childhood or adolescent booster vaccination in those previously eligible for vaccination during the infant, toddler, or preschool periods, to maintain direct protection and potentially enhance population immunity.

Fig 1

Seroprotection against serogroup C meningococci measured by proportions with serum bactericidal antibody (SBA) titers of ≥8. Shown is a comparison of current levels (2009) with the periods before (1996 to 1999) and shortly after (2000 to 2004) vaccine introduction. The applicable vaccine schedules to each age band at the time of the two postvaccine surveys are shown below the graphs. pre-sch, preschool.

Fig 2

Geometric mean titer (GMT) of serum bactericidal antibody (SBA) against group C meningococci. Shown are current levels (2009) compared with the period shortly after vaccine introduction (2000 to 2004).