ABSTRACT
Objective To analyze the levels of human serum antibody against Neisseria meningitidis serogroup C measured by serum bactericidal assay (SBA) and ELISA.Methods SBA and a modified ELISA were applied to measure the serum bactericidal titer and the specific concentration of immunoglobulin G (IgG) against meningoeoccal serogroup C in sera samples.Seventy-five sera were from healthy adults without undertaking vaccination while another 429 and 388pre- and post- vaccinated sera were from 143 infants and 194 young children immunized with conjugate vaccine or polysaccharide vaccine,respectively.Correlation between serum bactericidal titer and the concentration of specific IgG against meningococcal serogroup C was analyzed.Results The concentration of meningococcal serogroup C specific IgG in healthy adults showed a strong correlation (r=0.814 33,P＜0.001 ) with serum bactericidal titer through linear regression analysis.Weak correlation was observed between SBA titers and IgG concentration in pre vaccinated sera of infants and children ( conjugate/polysaccharide vaccine ) ( infants:r =0.140 64,P ＞ 0.100/r =0.2899,P＜0.05; children:r=0.540 40,P＜0.05/r=0.194 36,P＜0.05).After immunization with 2-dose conjugate vaccine in infants and 1-dose in children,a strong correlation between the two panels of results was observed (r=0.809 38,P＜0.001 and r=0.837 23,P＜0.001 respectively).However after immunization with polysaccharide vaccine,the correlation between serum bactericidal titer and concentration of specific IgG was weak (r＜0.500 00).Conclusion Among healthy adults and post vaccinated infants or young children immunized with conjugate vaccine,the concentration of specific IgG was comparable to the serum bactericidal titer against meningococcal serogroup C.However,it was not unfavorable to use ELISA as the principal means of measuring serum antibody responses to polysaccharide vaccine for infants under 1 year old.