Effectiveness analyses may underestimate protection of infants after group C meningococcal immunization.
BACKGROUND
Group C meningococcal conjugate-vaccine effectiveness in the United Kingdom declines from ~90% in the first year to 0% between 1 and 4 years after immunization in infants immunized at 2, 3, and 4 months of age and to 61% in toddlers given a single dose. Confidence intervals are wide, and the extent of protection is uncertain.


METHODS
Serum samples were obtained from children 3-5 years of age who were participants in a preschool booster-vaccine trial. Serum bactericidal activity was measured with human complement. Group C anticapsular antibody concentrations were measured by a radioantigen binding assay. Passive protection was analyzed in an infant rat bacteremia model.


RESULTS
Serum samples from UK children who had been immunized 2-3 years earlier as infants or toddlers had higher levels of radioantigen binding, bactericidal activity, and passive protection than did historical control serum samples from unimmunized children (P<.05). A higher proportion of children immunized as infants had serum bactericidal activity titers > or =1 : 4 (considered to be protective) than those immunized as toddlers (61% vs. 24%; P<.01), but there were no significant differences in the proportion of serum samples conferring passive protection (50% and 41%, respectively; P=.4).


CONCLUSIONS
We found no evidence of lower immunity in children immunized as infants than as toddlers. On the basis of serum bactericidal activity and/or passive protection, 40%-50% of both age groups are protected at 2-3 years after immunization, which was significantly greater than in unimmunized historical controls (<5%).
Vu
David M
DM
Children's Hospital Oakland Research Institute, Oakland, CA 94609, USA.
Kelly
Dominic
D
Heath
Paul T
PT
McCarthy
Noel D
ND
Pollard
Andrew J
AJ
Granoff
Dan M
DM
D000907:Antibodies, Bacterial / Q000097:blood; D002675:Child, Preschool; D004739:England; D006801:Humans; D007117:Immunization, Secondary; D008585:Meningitis, Meningococcal / Q000276:immunology / Q000517:prevention & control*; D022401:Meningococcal Vaccines / Q000008:administration & dosage* / Q000276:immunology*; D038542:Neisseria meningitidis, Serogroup C / Q000276:immunology*
D000907:Antibodies, Bacterial; D022401:Meningococcal Vaccines