Background: After the introduction of Haemophilus influenzae
type b (Hib) conjugate vaccines for infants there is a need to follow Hib
antibody levels to confirm that children are protected to the age when
"natural immunity" against invasive Hib infections has been acquired.
There has also been discussed if vaccination with the carrier protein could
increase antibodies against Hib in already primed children.
Methods: In 53 of 84 Swedish children immunized with 3 doses of a Hib-tetanus
toxoid conjugate vaccine (Hib-T) (NICHD, NIH, USA) in infancy, serum samples
were obtained before and one month after a booster dose of Vaccine against
Diphtheria and Tetanus(SBL Vaccin AB, Sweden). Antibodies against Hib were
measured with ELISA.
Results: Table. Serum antibodies
against Hib in 10-year-old children (n=53) vaccinated in infancy with Hib-T
before and after a booster dose of the carrier protein. Geometric mean (GM)
antibody concentrations (microgram/ml), range, and proportions of children(%)with antibodies above 0.15 and
1.0 microgram/ml.
Above
GM Range 0.15 1.0
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Pre 4.16 0.32 - 545.2 100 83
Post 4.30 0.39 - 749.0 100 87
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Conclusion: Children immunized with 3 doses of a Hib-tetanus toxoid vaccine in infancy still had high Hib antibody levels at 10 years of age. A booster dose of the carrier protein, tetanus toxoid, did not further increase Hib antibodies.