In the Netherlands the meningococcal serogroup C conjugate (MenCC) vaccine is administered as a single dose at 14 months. We evaluated the kinetics of isotype-specific antibodies in adults (n=21) after primary immunization with MenCC or secondary immunization with MenCC or plain MenC polysaccharide vaccine. Blood samples were collected prior to immunization and at 6 additional time points, from 3 to 25 days post-immunization. Secondary immunization resulted in 5-10-fold higher IgG titers compared to the primary immunization group, 25 days post-immunization. Prior to the secondary immunization, but 5 years after the first immunization, protective bactericidal antibodies and levels of MenC-specific IgG and IgM were still present. Furthermore, IgG antibodies present before secondary immunization were of higher avidity compared to antibodies produced one month after primary immunization. In addition, secondary immunization with nonconjugated MenC polysaccharide seemed to induce a higher IgG2 response compared to MenCC immunization. The kinetics of the observed secondary immune responses were not really faster than the observed primary responses. However, the rate of increase in antibodies seemed faster than the primary responses, representing a booster response. As the course of infection by Neisseria meningitidis can be very rapid, these data support the idea that sustainment of high antibody levels induced by MenCC are important for immediate protection.