[Immunogenicity of group A+C meningococcal polysaccharide conjugate vaccine in infants: A phase Ⅲ clinical trial...

Objective: To evaluate the immunogenicity of group A+C meningococcal polysaccharide conjugate vaccine in infants under 2 years old. Methods: From March 2017 to June 2018, 1 932 healthy infants in Biyang County, Henan Province, who were not vaccinated with meningococcal meningitis vaccine and whose axillary temperature was ≤37.0 ℃, were recruited as participants. The 3 months and 6-11 months old infants were allocated to the experiment group and the control group in a ratio of 1∶1. Infants aged 12-23 months were allocated to the 1-dose group, the 2-dose group and the control group in a ratio of 1∶1∶1, with 276 infants in each group. The infants in the experiment group were intramuscularly injected with freeze-dried group A+C meningococcal polysaccharide conjugate vaccine to be evaluated, and infants in the control group received intramuscular injection of commercially available freeze-dried group A+C meningococcal conjugate vaccine. The venous blood of infants was collected 30 days before the first dose and after the last dose of inoculation, and the antibody seroconversion of each group was determined and compared. Results: The completion rate of immunogenicity study was 95.2% (1 839/1 932). Before inoculation, there was no statistical difference in the geometric mean titer and positive rate of group A+C antibodies between the experiment group and the control group in 3 months and 6-11 months old infants (all P values >0.05). The geometric mean titers and positive rate of group A antibodies in the 1-dose group were higher than those in the control group (all P values <0.05), but there was no statistical difference between the 2-dose group and the control group (all P values >0.05) in infants aged 12-23 months. After inoculation, the differences (95%CI) in the positive conversion rate of group A+C antibodies between the experiment group and the control group were -0.12% (-6.01%-5.77%) and 0.82% (-4.23%-5.86%) in the 3 months old infants. At the age of 6-11 months, the differences were 6.75% (1.71%-11.79%) and -4.32% (-8.73%-0.08%), respectively. At the age of 12-23 months, the differences were 1.02% (-3.80%-5.83%) and -4.40% (-7.79%- -1.01%) in the 2-dose group and -7.22% (-12.90%- -1.54%) and -18.61% (-23.75%- -13.46%) in the 1-dose group, respectively. The geometric mean titers of group A+C antibodies in the 3 months old infants were 48.50 and 63.12, respectively, which had no significant difference from the control group (43.02 and 57.99, respectively) (both P values <0.05). The geometric mean titers of group A+C antibodies in the 6-11 months and 12-23 months old infants were 84.09 and 92.51 (2-dose group), which were higher than those in the corresponding control group (43.10 and 61.83, respectively) (all P values <0.001). Conclusion: Group A+C meningococcal conjugate vaccine has good immunogenicity in infants under 2 years old.