Although immunization programs with @entity327 type b (Hib) conjugate vaccines have dramatically reduced disease incidence, few data are available regarding the duration of protection after vaccination. We measured serum anti- @entity11872 (PRP) levels in healthy 4- to 5- year-old @entity1 previously given 4 doses of @entity21934 vaccine (at 2, 4, 6, and 18 months) or 1 dose of PRP-D vaccine (at 19 months) during clinical trials to assess antibody persistence. Concurrent with other preschool immunizations, half of the @entity1 were randomly assigned to receive a @entity21934 booster immunization to assess responsiveness. Among 136 subjects who were primed with PRP-D, the baseline geometric mean concentration of antibody was 0.7 microg/mL (95% CI 0.5 to 0.9). Concentrations were <0.15 microg/mL in 24 (17.6%) subjects. Among 212 @entity1 who were primed with @entity21934 , the geometric mean concentration was 2.2 microg/mL (95% CI 1.9 to 2.5) (P <.001). Only 2 (0.9%) had concentrations <0.15 microg/mL. Four weeks after @entity21934 immunization, geometric mean concentrations had increased to 98.4 and 102.0 microg/mL, respectively. Responses were strong even in those with low or undetectable preimmunization antibody levels. Spontaneous increases in antibody levels were seen in 9 (5.2%) of 172 subjects not given additional @entity21934 . We concluded that among 4- to 5-year-olds, anti-PRP levels remained above 0.15 microg/mL in nearly all @entity1 after @entity21934 priming and in most after PRP-D priming, and that both groups were able to respond vigorously to restimulation, consistent with persistent immune memory.

Extended follow-up of antibody levels and antigen responsiveness after 2 XXXX type b conjugate vaccines.

@entity11872 :: ('MESH:C008984', 'Chemical') :: ['polyribosylribitol phosphate'] @entity1 :: ('9606', 'Species') :: ['children'] @entity327 :: ('727', 'Species') :: ['Haemophilus influenzae'] @entity21934 :: ('MESH:D005955', 'Disease') :: ['PRP-T']
@entity327 :: (727,Species) :: ['Haemophilus influenzae']
