A Phase III Clinical Trial of Immunogenicity and Safety of Meningococcal A and C Polysaccharide Conjugate Vaccine in Infants Aged 3-5 Months.

Background/Objectives: This study aimed to evaluate the immunogenicity and safety of a Meningococcal A and C Polysaccharide Conjugate Vaccine in 3-5-month-old infants. A single-center, randomized, blinded, positive-controlled phase III clinical trial was conducted in Binyang County, Guangxi Zhuang Autonomous Region, China. Infants aged 3-5 months were randomly assigned to the experimental or control group at a 1:1 ratio. Both groups received 3 primary doses with a 1-month interval between each dose, and a booster dose administered at 18 months of age. Seroconversion rate, seropositivity rate, and GMT of bactericidal antibodies against Neisseria meningitidis groups A and C were assessed, along with adverse reactions within the full course of primary immunization and 30 days after booster immunization. Results: After primary immunization, in the experimental group's pre-vaccination antibody-negative infants, seroconversion rates for groups A and C exceeded 90%, with antibody fold increases over 90 times; its seroconversion rates and GMT were non-inferior to the control group. Before the 18-month booster, the experimental group's group A and C antibody seropositivity rates dropped to approximately 70% and 30% (slightly higher than the control), respectively. After booster immunization, the antibody levels against groups A and C were significantly higher than those before the booster and the positive rates and GMT levels of the two groups were similar. Adverse reactions were mainly solicited systemic ones (fever most common), with no statistical difference between groups. Conclusions: The experimental vaccine shows great immunogenicity and safety in infants aged 3-5 months and is non-inferior to the control vaccine. In the booster immunization phase of the control group, sequential vaccination with vaccines from different manufacturers was adopted, and the immunogenicity was good.