Validation of the serum bactericidal assay for measurement of functional antibodies against group B meningococci associated with vaccine trials

Provisional licensure of the trial vaccine, MeNZB™, required demonstration of immune responses in vaccines, as measured by a validated Serum Bactericidal Assay (SBA). Reported are the investigations undertaken to define test parameters, lower limits of quantitation and measurement of SBA reproducibility. Results helped to formulate the operating procedure for the measurement of serum bactericidal antibodies during six age-group MeNZB™ vaccine trials. The lower limit of quantitation was determined as a titre of 4. A four-fold rise in antibody (sero-conversion) from a pre-vaccination titre of 2 (<4) required a minimum post-vaccination titre of 8, a more stringent measurement than has been used in other published studies.