Characterization and vaccine-induced immunogenicity of a re-emerging Neisseria meningitidis serogroup Y in Tianjin, China.

Abstract

INTRODUCTION: Since the incorporation of serogroups A and C meningococcal vaccines into China's national immunization program, the epidemiological profile of Neisseria meningitidis (Nm) has shifted toward serogroups not covered in routine vaccination, particularly Y and B. This study assessed the immunogenicity of the quadrivalent meningococcal polysaccharide vaccine (MPSV4) and the quadrivalent meningococcal polysaccharide conjugate vaccine (MCV4) against a newly identified serogroup Y strain in Tianjin, and characterized its clinical presentation, laboratory features, and antimicrobial resistance profile. METHODS: Epidemiological investigation and laboratory testing were undertaken to document the clinical manifestations, molecular characteristics, and antimicrobial susceptibility of the isolate. Serum bactericidal activity (SBA) was evaluated in a murine model. Fifty mice were randomized into five groups and immunized with MCV4, MPSV4-A, MPSV4-B, MPSV4-C, or normal saline. Vaccinations were administered at 14-day intervals for a total of three doses. Serum samples were collected 14&#xa0;days after each immunization for SBA analysis. RESULTS: The bacterial isolate, obtained from a case of invasive meningococcal disease, was confirmed as serogroup Y and classified as sequence type ST-18108. Antimicrobial susceptibility testing against 12 agents revealed resistance solely to nalidixic acid, while susceptibility was retained to seven agents. In SBA assay, MCV4 induced the strongest response, with a geometric mean titer of 294 and a 100&#xa0;% seroconversion rate after the third dose, exceeding responses observed in all MPSV4 groups. Antibody titers in the MCV4 cohort were significantly higher than those in the MPSV4-A, MPSV4-B, and control groups after both the second and third immunizations (P&#xa0;<&#xa0;0.05). Furthermore, within the MCV4 group, titers rose significantly between the second and third doses (P&#xa0;=&#xa0;0.004), whereas no significant increase was observed in MPSV4 groups (P&#xa0;>&#xa0;0.05). CONCLUSIONS: Compared with MPSV4, MCV4 generated stronger bactericidal antibody responses and provided superior protective immunity against serogroup Y in a mouse model, which lays the groundwork for further development of meningococcal vaccines. Moving forward, studies should incorporate a broader range of bacterial strains, larger sample sizes, and ultimately human clinical trials to confirm and extend these findings.