Developments during the past decade have renewed hopes for solving this seemingly intractable problem. Knowledge of the meningococcal genome has led to the identification of novel antigens that have been incorporated into the NMB vaccines now being studied in clinical trials. However, it remains unclear whether these vaccines will provide sufficient immunogenicity in infants as well as wide-ranging coverage. This review highlights the evolution of meningococcal vaccines in general and discusses strategies being used to overcome the barriers to developing vaccines against NMB. Epidemiology of N. meningitidis Infection Meningococcal disease is a global health problem. The World Health Organization estimates that there are 1.2 million cases of invasive meningococcal disease and 135,000 related deaths annually. 3 Although the disease occurs sporadically in industrialized countries, with an incidence of 0.35 cases per 100,000 population in the United States and of 1.01 per 100,000 in Europe (ranging from 0.25 to 4.4 per 100,000 in Italy and Malta, respectively), 4 the major disease burden is in the nonindustrialized countries. A recent epidemic in Nigeria resulted in 4164 cases and 171 deaths in 1 week alone. 5 The meningococcus is pathogenic only in humans. It colonizes the nasopharynx asymptomatically in up to 40% of the adult population but occasionally causes invasive disease. When the infection is classified according to the polysaccharide capsule surrounding the bacterium, only six capsular groups (A, B, C, W-135, X, and Y) are associated with invasive disease. 6 The epidemiology of disease caused by these groups varies: group A is responsible for large epidemics in Africa, in which the incidence approaches 1000 cases per 100,000 population (and may involve environmental factors), whereas groups B and C cause disease predominantly in industrialized and newly industrialized countries. 2,6 Recently, groups W-135 and X (predominantly in Africa) and group Y (in the United States and other countries) have emerged as important disease-causing isolates.