Dynamic evaluation of antibodies against serogroup A, C, Y and W135 strains in healthy adults im-munized with one dose of quadrivalent meningococcal polysaccharide vaccine
Objective To dynamically analyze the antibodies with regard to in vitro serum bacteri-cidal activity and the quantity of IgG in healthy adults received one dose of immunization with ACYW 135 me-ningococcal polysaccharide vaccine .To investigate the term of protection with polysaccharide vaccine and the correlation between bactericidal titer and IgG concentration .Methods Twenty healthy adults were given one dose of immunization with quadrivalent meningococcal polysaccharide vaccine .Serum samples were col-lected before and after vaccination at specific time points .Test for serum bactericidal activity （ SBA ） and quantitative ELISA were performed to detect bactericidal titers and IgG concentrations in serum samples .Re-sults Certain levels of antibodies against capsular polysaccharides of serogroup A , C, Y and W135 strains had already existed prior to immunization .Moreover, bactericidal titers against serogroup A , Y and W135 strains except serogroup C strain were relatively high .Specific IgG concentrations and bactericidal titers for all serogroup stains were significantly increased on day 15 after vaccination （P〈0.05）, and then sustained at a high level during a time period from day 30 to day 160.Both IgG concentrations and bactericidal titers dropped to the levels similar to that before preimmunization in about 3 years.No significant correlation was observed between bactericidal titers and IgG concentrations （r〈0.3, P〉0.05）.However, a close correla-tion was demonstrated between GMTs and GMCs of serum samples （r〉0.7, P〈0.05）.Conclusion The geometric mean titers （ GMTs） and geometric mean concentrations （ GMCs） of serum samples collected be-fore and after vaccination at different time points were reliable and consistent parameters for the evaluation of vaccine .The term of protection of quadivalent meningococcal polysaccharide vaccine was about 3 years upon a single dose of immunization . 
 
Key words: 
Serogroup ACYW135 meningococcal polysaccharide vaccine;  Serum bactericidal activity （SBA） ;  Enzyme-linked immunoabsorbent assay （ELISA）