We conducted a systematic review and meta-analysis of randomised controlled trials in which infants were randomised to receive meningococcal or pneumococcal conjugate vaccines along with Hib-TT. Trials of licensed vaccines with different carrier proteins were included for group C meningococcal (MenC), quadrivalent ACWY meningococcal (MenACWY), and pneumococcal vaccines.
Twenty-three trials were included in the meta-analyses. Overall, administration of MenC-CRM in a 2 or 3 dose schedule resulted in a 45% reduction in Hib antibody concentrations (GMR 0.55, 95% CI 0.49–0.62). MenACWY-CRM boosted Hib antibody responses by 22% (GMR 1.22, 95% CI 1.06–1.41) whilst pneumococcal CRM conjugate vaccines had no impact on Hib antibody responses (GMR 0.91, 95% CI 0.68–1.22).
The effect of CRM protein-polysaccharide conjugate vaccines on Hib antibody responses varies greatly between vaccines. Co-administration of a CRM conjugate vaccine can produce either positive or negative effects on Hib antibody responses. These inconsistencies suggest that CRM itself may not be the main driver of variability in Hib responses, and challenge current perspectives on this issue.