Background: The incidence of meningococcal disease is highest in children under 2 years of age, yet no vaccine for this population is currently available in the US. Previous studies show that HibMenCY-TT was immunogenic for Hib, MenC and MenY in infants, following four doses given at 2, 4, 6, and 12-15 months of age, with protective levels of antibodies persisting in the majority of subjects 1 year after the 4th dose vaccination.
Objectives: To determine the persistence of protective antibodies 3 years after a 4th dose vaccination in terms of anti-PRP concentrations and hSBA titers against MenC and MenY.
Methods: In the previous study (NCT00129129), 606 infants were randomized 1:1 to receive HibMenCY-TT or Hib-TT at 2, 4, and 6 months of age. At 12-15 months, subjects who received HibMenCY-TT received a 4th dose of HibMenCY-TT (HibMenCx4); Hib-TT-primed subjects were re-randomized 1:1 to receive one dose of HibMenCY-TT (HibMenCYx1) or Hib-TT (Hibx4). In this extension study (NCT00359983), antibody persistence was assessed 3 years later in 201 subjects. Primary endpoints were anti-PRP ≥0.15 mcg/mL and hSBA titers against MenC and MenY ≥1:8.
Results: Three years after the 4th dose vaccination:
- Subjects with anti-PRP concentrations ≥0.15 mcg/mL (95% CI): HibMenCYx4= 98.4% (91.2-100); HibMenCYx1= 100% (90.3-100); Hibx4= 92.9% (76.5-99.1).
- Subjects with hSBA MenC titers ≥1:8 (95% CI): HibMenCYx4= 81.4% (69.1-90.3); HibMenCYx1= 57.1% (39.4-73.7); Hibx4= 11.1% (2.4-29.2).
- Subjects with hSBA MenY titers ≥1:8 (95% CI): HibMenCYx4= 67.2% (53.7-79.0); HibMenCYx1= 55.9% (37.9-72.8); Hibx4= 15.4% (4.4-34.9).
Conclusions: Nearly all (>92.9%) children in all groups had anti-PRP concentrations ≥0.15 mcg/mL. The majority of children who received four doses of HibMenCY-TT retained protective titers against MenC and MenY, and statistically significantly more of these children had hSBA MenC titers ≥1:8, compared with children who received a single dose.