In order to plan for the wide-scale introduction of meningococcal C conjugate (MCC) vaccine for United Kingdom children up to 18 years old, phase II trials were undertaken to investigate whether there was any interaction between MCC vaccines conjugated to tetanus toxoid (TT) or a derivative of diphtheria toxin (CRM 197 ) and diphtheria-tetanus vaccines given for boosting at school entry or leaving. Children (n ‫؍‬ 1,766) received a diphtheria-tetanus booster either 1 month before, 1 month after, or concurrently with one of three MCC vaccines conjugated to CRM 197 or TT. All of the MCC vaccines induced high antibody responses to the serogroup C polysaccharide that were indicative of protection. The immune response to the MCC-TT vaccine was reduced as a result of prior immunization with a tetanus-containing vaccine, but antibody levels were still well above the lower threshold for protection. Prior or simultaneous administration of a diphtheria-containing vaccine did not affect the response to MCC-CRM 197 vaccines. The immune responses to the carrier proteins were similar to those induced by a comparable dose of diphtheria or tetanus vaccine. The results also demonstrate that, for these conjugate vaccines in these age groups, both standard enzyme-linked immunosorbent assays and those that measure high-avidity antibodies to meningococcal C polysaccharide correlated equally well with assays that measure serum bactericidal antibodies, the established serological correlate of protection for MCC vaccines.In November 1999, the United Kingdom introduced conjugate vaccines against meningococcal serogroup C disease (MCC vaccines) into its immunization schedule for infants, with promising early reports of efficacy (18). The vaccines were also offered to all children between 1 and 17 years of age as a catch-up program that started in November 1999 and was completed within a year. The evidence of safety and immunogenicity of the MCC vaccines in these age groups was obtained from phase II trials conducted in the United Kingdom and sponsored by the Department of Health. Following promising results of early trials using the 2-, 3-, and 4-month schedule in United Kingdom infants (16), the Department of Health sponsored a comprehensive clinical trials program to evaluate the performance of candidate MCC vaccines in toddlers, children starting school, children leaving school, and young adults (12).One concern was the potential for interaction between the MCC vaccines, which contained either tetanus toxoid (TT) or the CRM 197 derivative of diphtheria toxin as the protein carrier, and the diphtheria and tetanus vaccines given as booster doses at school entry (DT) or school leaving (Td). To address these concerns, trials were conducted in which children received MCC vaccine a month before or after, or at the same time as, their DT or Td booster vaccine. Humoral immune responses against DT and MCC antigens were assessed following each vaccination.Since it was anticipated that licensure of the MCC vaccines would be based on immunogenic...

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The significance of reduced antibody responses to the Haemophilus influenzae type b (Hib) component of acellular pertussis-containing combination vaccines (DTaP-Hib) is unclear. A DTaP-Hib vaccine evaluated in infants vaccinated at ages 2, 3, and 4 months showed reduced anti-Hib polysaccharide IgG (geometric mean concentration [GMC], 1.23 microgram/mL; 57%, >1.0 microgram/mL). Polyribitolribosyl phosphate (PRP) and Hib conjugate (PRP-T) vaccine given as a booster during the second year of life was evaluated for the presence of immunological memory. After boosting, most children achieved anti-PRP IgG >1.0 microgram/mL, although the GMC was higher with PRP-T (88.5 microgram/mL) than with PRP vaccine (7.86 microgram/mL, P<.001). The GMC of the PRP group was higher than anticipated for naive PRP recipients of the same age. PRP-specific IgG avidity was significantly higher after boosting than after priming, providing further evidence for the generation of memory. Despite reduced immunogenicity, DTaP-Hib combination vaccines appear to prime for immunologic memory.