Protection against group B meningococcal disease: evaluation of serotype 2 protein vaccines in a mouse bacteremia model.

A mouse bacteremia model was used to evaluate the immunogenicity and protection against challenge provided by five different meningococcal serotype 2 vaccines. Mice vaccinated with serotype 2 protein vaccines had levels of bacteremia reduced by at least 100-fold after challenge with group B serotype 2 miningococci. Mice vaccinated with serotype 2 protein vaccine and challenged with group C serotype 2 meningococci showed 10-fold or less reduction in bacteremia. Vaccines were primarily serotype specific since no increase in protection was observed after challenge with either group B serotype 4 or group C nontypable meningococci. Serotype 2 antibody levels, measured by the bactericidal assay and the enzyme-linked immunosorbent assay 3 weeks after immunization, demonstrated a graded dose-response which correlated with protection up to 40 weeks after vaccination with a single 10- or 25-micrograms dose of serotype 2 protein vaccine. A 1-microgram booster dose of serotype 2 vaccine, given 2 weeks after primary immunization, significantly increased both bactericidal (P less than 0.01) and enzyme-linked immunosorbent assay (P less than 0.02) titers. The data obtained from the mouse bacteremia model indicate that serotype 2 protein vaccines are stable and immunogenic, and protect mice against challenge with group B serotype 2 meningococci.