Demonstration of immunologic memory using serogroup C meningococcal glycoconjugate vaccine.

BACKGROUND: Studies of glycoconjugate vaccines have traditionally used an immune challenge with a plain polysaccharide vaccine to demonstrate immunologic memory. Plain polysaccharide vaccines are poorly immunogenic in children and can induce subsequent immunologic hyporesponsiveness. We therefore assessed the use of glycoconjugate vaccines as an alternative method of demonstrating immunologic memory. METHODS: Children immunized with hepatitis B vaccine or serogroup C meningococcal glycoconjugate vaccine (MenCC) at age 2, 3, 4 months received a plain polysaccharide meningococcal serogroup A/C vaccine (MenACP) or MenCC at age 12 months. A post hoc analysis of serum bactericidal activity responses to MenCC assessed whether this differed in MenCC primed and MenCC naive infants. RESULTS: MenCC primed children displayed higher geometric mean serum bactericidal titers than MenCC naive children following MenACP (1518 compared with 30; P = 0.003). A similar difference was seen after a dose of MenCC to toddlers (MenCC primed: 8663, MenCC naive: 710; P < 0.001). The latter comparison became a borderline significance after adjusting for higher pretoddler immunization serum bactericidal geometric mean titers in the MenCC primed group (P = 0.068). CONCLUSIONS: Administration of glycoconjugate vaccines provides an important alternative method of demonstrating immunologic memory, avoiding the use of plain polysaccharide vaccines that are potentially deleterious in children. This has implications for the design of all future clinical trials of glycoconjugate vaccines.

Haemophilus influenzae type b vaccine failure in children is associated with inadequate production of high-quality antibody.

BACKGROUND: Despite the excellent immunogenicity of Haemophilus influenzae type b (Hib) conjugate vaccines, breakthrough cases of Hib disease still affect a small proportion of vaccinated children in the United Kingdom. We performed a retrospective study to compare the avidity of antibody directed against the Hib polysaccharide capsule (PRP) in children who experienced Hib vaccine failure in the United Kingdom among 3 historical cohorts and with age-matched healthy control subjects. METHODS: Serum samples from vaccinated children with invasive Hib disease were collected beginning in 1992 as part of enhanced surveillance for Hib disease following vaccine introduction. A total of 251 children who experienced Hib vaccine failure were identified from 3 historical cohorts (1992-1995, 1996-1999, and 2000-2003). The anti-PRP antibody concentration and avidity from healthy age-matched control subjects was obtained for the 3 contemporary time points (1995, 1999, and 2002). Serum anti-PRP antibody concentration was measured in each of the samples using a standard Hib ELISA, and antibody avidity was determined using thiocyanate elution. RESULTS: Within the first 60 days after disease onset, there was no change in the anti-PRP antibody avidity, and there was no statistically significant difference in the geometric mean Hib antibody avidity over the 3 study periods. However, the children who experienced Hib vaccine failure had significantly lower Hib antibody avidity than did healthy control subjects, despite a marked antibody response following infection. CONCLUSIONS: Children who experience Hib disease despite vaccination appear to have a defect in immunological priming, leading to a qualitative difference in Hib-specific memory B cells. Low anti-PRP antibody avidity decreases the functional activity of anti-PRP antibody in the sera of these children experiencing vaccine failure, leading to disease susceptibility.