Extended follow-up of antibody levels and antigen responsiveness after 2 Haemophilus influenzae type b conjugate vaccines.
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.
Scheifele
D W
DW
Vaccine Evaluation Center, BC's Children's Hospital, Vancouver, British Columbia, Canada.
Halperin
S A
SA
Guasparini
R
R
Meekison
W
W
Pim
C
C
Barreto
L
L
D000914:Antibodies, Viral / Q000378:metabolism*; D002170:Canada; D002675:Child, Preschool; D005260:Female; D018073:Haemophilus Vaccines / Q000008:administration & dosage*; D006801:Humans; D007115:Immunization Schedule; D007156:Immunologic Memory; D008297:Male; D018709:Statistics, Nonparametric; D018074:Vaccines, Conjugate
D000914:Antibodies, Viral; D018073:Haemophilus Vaccines; D018074:Vaccines, Conjugate