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

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 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 % 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 < 0.05). Furthermore, within the MCV4 group, titers rose significantly between the second and third doses (P = 0.004), whereas no significant increase was observed in MPSV4 groups (P > 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.