Impact of meningococcal serogroup C conjugate vaccines on carriage and herd immunity.
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.
Maiden
Martin C J
MC
Dept. of Zoology, John Radcliffe Hospital, Oxford University, Oxford, United Kingdom. martin.maiden@zoo.ox.ac.uk
Ibarz-Pavón
Ana Belén
AB
Urwin
Rachel
R
Gray
Stephen J
SJ
Andrews
Nicholas J
NJ
Clarke
Stuart C
SC
Walker
A Mark
AM
Evans
Meirion R
MR
Kroll
J Simon
JS
Neal
Keith R
KR
Ala'aldeen
Dlawer A A
DA
Crook
Derrick W
DW
Cann
Kathryn
K
Harrison
Sarah
S
Cunningham
Richard
R
Baxter
David
D
Kaczmarski
Edward
E
Maclennan
Jenny
J
Cameron
J Claire
JC
Stuart
James M
JM
D000293:Adolescent; D000328:Adult; D002353:Carrier State / Q000453:epidemiology*; D003430:Cross-Sectional Studies; D006801:Humans; D032521:Immunity, Herd / Q000276:immunology*; D032541:Mass Vaccination; D008589:Meningococcal Infections / Q000453:epidemiology* / Q000517:prevention & control; D022401:Meningococcal Vaccines / Q000276:immunology*; D009345:Neisseria meningitidis / Q000145:classification / Q000276:immunology; D038542:Neisseria meningitidis, Serogroup C / Q000276:immunology* / Q000472:pathogenicity; D012703:Serotyping; D006113:United Kingdom / Q000453:epidemiology
D022401:Meningococcal Vaccines; C410218:serogroup C meningococcal conjugate vaccine