Objective To optimize the
serum bactericidal assay (SBA) , detect and analyze the bactericidal antibody level against
Neisseria meningitidis serogroup C
strains after divalent
polysaccharide (A plus C)
vaccine immunization .
Methods Two
Neisseria meningitidis serogroup C
strains ,
vaccine candidate
strain (C11) and
epidemic strain (053442), were selected as targets. The national
Neisseria meningitidis standardized
serum was used as reference
serum . Pel-Freez
infant rabbit complements was available. The optimized SBA
method was used to detect bactericidal antibody against
strain C11 and 053442 for 122 pairs of sera before and after
immunization with a divalent
polysaccharide (A and C)
vaccine . Results The
strain C11 and 053442 both could be used as targeted
strain for SBA. The optimized concentration of targeted
strain was achieved when a whole-
cell suspension of 0.35 A at 600 nm was diluted 4×104 times. Before
immunization , SBA geometric mean titers(GMT) of 122 sera against
strain C11 and 053442 were 1 1.75 and 12.63 respectively, and the protective rates were 9.8% and 17.2% respectively. After
immunization , the GMTs and the protective rates of 122 sera both
rose significantly (P<0.01), the GMTs against
strain C11 and 053442 were 1483.73 and 1412.57 respectively. The protective rates against
strain C11 and 053442 were 100% and 95.9% respectively. Conclusion
Immunization with a divalent
polysaccharide (A and C)
vaccine could elevate remarkably the
population SBA titer against
Neisseria meningitidis serogroup C
strains of different subtypes, but the
surveillance of
vaccine effect against different targeted
strains remains necessary.