The hyperferremic mouse model for the evaluation of the effectiveness of VA-MENGOC-BC against Neisseria meningitidis B clinical isolates.

VA-MENGOC-BC is a vaccine against B and C serogroups of Neisseria meningitidis. Its effectiveness at population level has been shown after the application of the vaccine in Cuba, Brazil, Argentina and Colombia. In vitro assays are not always able to reproduce the microorganism-host relationships and this makes it necessary to compile and standardize results obtained in animal models to extrapolate them with a greater degree of safety for humans. We evaluated the effectiveness of VA-MENGOC-BC against Neisseria meningitidis group B isolates from clinically ill patients in Latin America (Argentina, B not typeable: P1; Chile, not typed; Colombia, B4:P1.15 and Cuba B4:P1.15) using Balb/cJ mice treated with iron to make them susceptible to Neisseria meningitidis. The lethal median dose of each strain and of two others that were not included in challenge assays (Brazil: P1.15 and Argentina, B2b:P1.10) were determined. Results were 2.68 x 10(6), 3.16 x 10(7), 1.98 x 10(8), 1.28 x 10(9), 6.42 x 10(6) and 3.88 x 10(7) colony forming units (CFU), respectively. Non-immunized animals and mice treated with one and two doses of VA-MENGOC-BC were challenged with 10(3)-(10) CFU. Protection ranged from 30 to 100% with one dose and was equal to or higher than 70% with the two-dose immunization schedule. A significant protection could not be observed against the Colombian isolate from the lethality point of view, but the mean time of survival lengthened in immunized animals in relation to the controls. The applied inoculum of this strain was much higher (505 x LD50) than the remaining ones. The protection conferred was evident; nevertheless, more data are needed to determine how relevant the results are to humans.