Extended follow-up of antibody levels and antigen responsiveness after 2 Haemophilus influenzae type b conjugate vaccines.
J Pediatr
; 135(2 Pt 1): 240-5, 1999 Aug.
Article
in En
| MEDLINE
| ID: mdl-10431120
ABSTRACT
Although immunization programs with Haemophilus influenzae 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-polyribosylribitol phosphate (PRP) levels in healthy 4- to 5- year-old children previously given 4 doses of PRP-T 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 children were randomly assigned to receive a PRP-T 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 children who were primed with PRP-T, 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 PRP-T 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 PRP-T. We concluded that among 4- to 5-year-olds, anti-PRP levels remained above 0.15 microg/mL in nearly all children after PRP-T priming and in most after PRP-D priming, and that both groups were able to respond vigorously to restimulation, consistent with persistent immune memory.
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Collection:
01-internacional
Database:
MEDLINE
Main subject:
Immunization Schedule
/
Haemophilus Vaccines
/
Immunologic Memory
/
Antibodies, Viral
Type of study:
Clinical_trials
Limits:
Child, preschool
/
Female
/
Humans
/
Male
Country/Region as subject:
America do norte
Language:
En
Journal:
J Pediatr
Year:
1999
Document type:
Article
Affiliation country:
Canada