A randomized, multicenter, open-label clinical trial to assess the immunogenicity of a meningococcal C vaccine booster dose administered to children aged 14 to 18 months.

BACKGROUND: A booster meningococcal C (MenC) vaccine dose is recommended after the first year of life. The objective of this study was to assess its immunogenicity and factors that modify the immunoresponse. METHODS: An open label study in which 389 children 14 to 18 months of age, previously primed with 3 doses of a MenC vaccine conjugated with CRM197 (MenC-CRM) or with 2 doses of a MenC vaccine conjugated with tetanus toxoid (MenC-TT), were randomized to be boosted with either of these vaccines and a DTaP-IPV-Hib vaccine at the same time. Immunogenicity against MenC and Haemophilus influenzae type b was assessed before and 1 month after the booster dose. RESULTS: Before the second year booster, 44.9% of the studied children had MenC bactericidal (SBA) seroprotection rate of > or =1:8, with no differences related to the vaccine used for priming, whereas the anti Hib antibody concentration was higher in children primed with the MenC-TT (0.59; 95% CI: 0.49-0.71 vs. 0.39; 95% CI: 0.32-0.48).One month after the MenC vaccine booster 99.5% of the children had SBA > or =1:128. Children primed with MenC-TT reached higher SBA titers: 6520 (95% CI: 5359-7932) than those primed with MenC-CRM: 1903 (95% CI: 1600-2262). Children primed with MenC-CRM had SBA titers of 2061 (95% CI: 1599-2627) when boosted with MenC-TT and 1746 (95% CI: 1378-2213) when boosted with MenC-CRM. Children primed with MenC-TT had SBA titers of 6786 (95% CI: 5023-9167) and 6278 (95% CI: 4841-8144) when boosted with MenC-TT or MenC-CRM. There was no difference in the PRP antibody concentration after boosting. CONCLUSIONS: A booster MenC dose induces high SBA and anti Hib response with over 99% of children seroprotected. Children primed with a MenC-TT vaccine reached SBA titers 3.5 times higher no matter which vaccine was used for boosting.