ANTIBODY PERSISTENCE AND HAEMOPHILUS-INFLUENZAE TYPE-B CARRIAGE AFTERINFANT IMMUNIZATION WITH PRP-T

Objectives-To assess the persistence of serum Haemophilus influenzae t ype b antibodies and the prevalence of H influenzae type b carriage in a group of preschool age children previously vaccinated in infancy. D esign-Names were randomly selected from immunisation records. Families were visited on five occasions over a period of 12 months and throat swabs were taken from all family members present, with blood obtained from children at the first and last visits. Results-One hundred and fi fty three children at a median age of 3.6 years had a geometric mean t itre (GMT) of 1.06 mu g/ml (95% CI 0.80 to 1.38). Eight per cent had a n undetectable antibody concentration, received a booster dose of plai n PRP vaccine, and responded with concentrations > 2 mu g/ml. GMT at 4 .5 years of age was 0.89 mu g/ml (0.69 to 1.16). Twelve children who h ad been exposed to H influenzae had a GMT of 4.7 v 0.8 mu g/ml for tho se without exposure. Conclusions-Accelerated immunisation against H in fluenzae without a second year booster results in persistence of satis factory serum concentrations of antibody to 4.5 years of age. In those with undetectable antibody, immunological memory may still be present .