The induction of immunological memory to serogroup A and C polysaccharides in UK infants
immunized with three doses of a meningococcal A/C oligosaccharide CRM197 conjugate
vaccine was investigated. Forty UK infants vaccinated previously with three doses of a
meningococcal A/C oligosaccharide-CRM197 conjugate vaccine at 2, 3 and 4 months of age,
were revaccinated at a mean age of 145·6 weeks with either a 10 or 50 μg dose of licensed
meningococcal A/C polysaccharide vaccine. Serogroup-specific antibody and serum bactericidal
antibody (SBA) responses were measured by enzyme-linked immunosorbent assay and serum
bactericidal assays, respectively. Following challenge, anti-serogroup A and C polysaccharide
antibody levels rose from pre-booster geometric mean concentrations (GMC) of 3·1 and 2·1
μg/ml respectively to 19·6 and 21·0 μg/ml 1 month post-booster. Serum bactericidal antibody
geometric mean titres (GMTs) for serogroups A and C increased 156- and 113-fold from 2·1
and 7·1 pre-booster respectively to 327·4 and 800·7 post-booster. A serogroup A control group
of 45 children received a 10 μg dose of licensed meningococcal A/C polysaccharide vaccine
(with no prior history of serogroup A vaccination) had serogroup A SBA GMTs of 2·3 pre-
vaccination rising to 8 post-vaccination with corresponding GMCs of 0·8 and 10·8 μg/ml.
These rises in SBA following serogroup A/C conjugate vaccination are indicative of
immunological priming.