Impact of meningococcal serogroup C conjugate vaccines on carriage and herd immunity

Martin C.J. Maiden, Ana Belén Ibarz-Pavón, Rachel Urwin, Stephen J. Gray, Nicholas J. Andrews, Stuart C. Clarke, A. Mark Walker, Meirion R. Evans, J. Simon Kroll, Keith R. Neal, Dlawer A.A. Ala'Aldeen, Derrick W. Crook, Kathryn Cann, Sarah Harrison, Richard Cunningham, David Baxter, Edward Kaczmarski, Jenny MacLennan, J. Claire Cameron, James M. Stuart

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Background. In 1999, meningococcal serogroup C conjugate (MCC) vaccines were introduced in the United Kingdom for those under 19 years of age. The impact of this intervention on asymptomatic carriage of meningococci was investigated to establish whether serogroup replacement or protection by herd immunity occurred. Methods. Multicenter surveys of carriage were conducted during vaccine introduction and on 2 successive years, resulting in a total of 48,309 samples, from which 8599 meningococci were isolated and characterized by genotyping and phenotyping. Results. A reduction in serogroup C carriage (rate ratio, 0.19) was observed that lasted at least 2 years with no evidence of serogroup replacement. Vaccine efficacy against carriage was 75%, and vaccination had a disproportionate impact on the carriage of sequence type (ST)-11 complex serogroup C meningococci that (rate ratio, 0.06); these meningococci also exhibited high rates of capsule expression. Conclusions. The impact of vaccination with MCC vaccine on the prevalence of carriage of group C meningococci was consistent with herd immunity. The high impact on the carriage of ST-11 complex serogroup C could be attributed to high levels of capsule expression. High vaccine efficacy against disease in young children, who were not protected long-term by the schedule initially used, is attributed to the high vaccine efficacy against carriage in older age groups.

Original languageEnglish
Pages (from-to)737-743
Number of pages7
JournalJournal of Infectious Diseases
Issue number5
Publication statusPublished - 1 Mar 2008

Bibliographical note

Funding Information:
Received 9 August 2007; accepted 14 September 2007; electronically published 13 February 2008. Presented in part: 14th International Pathogenic Neisseria Conference, Milwaukee, WI, 6–13 September 2004 (first abstract, first session, vaccinology). Potential conflicts of interest: none reported. Financial support: the Wellcome Trust (grant 062057; sampling in England and Wales and molecular characterization of isolates); the Chief Scientist Office of the Scottish Executive Health Department (sampling in Scotland); and the Meningitis Trust (questionnaire).


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