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Antibody persistence and Haemophilus influenzae type b carriage after infant immunisation with PRP-T
P T Heath1, J Bowen-Morris, D Griffiths
1Department of Paediatrics, John Radcliffe Hospital, Oxford.
Insights
Accelerated Haemophilus influenzae type b (Hib) vaccination without a booster maintains protective antibody levels in preschool children up to 4.5 years old. Immunological memory may persist even with undetectable antibody concentrations.
Area of Science:
- Immunology
- Vaccinology
- Pediatric Infectious Diseases
Background:
- Haemophilus influenzae type b (Hib) infections pose a significant risk to young children.
- Infant vaccination schedules aim to establish long-term immunity against Hib.
- Assessing antibody persistence and carriage is crucial for evaluating vaccine effectiveness.
Purpose of the Study:
- To evaluate the duration of serum antibodies against Haemophilus influenzae type b (Hib) in preschool children.
- To determine the prevalence of Hib carriage in vaccinated children and their families.
- To assess the impact of accelerated infant immunization without a booster on long-term immunity.
Main Methods:
- Random selection of children from immunization records.
- Longitudinal study involving five family visits over 12 months.
- Collection of throat swabs for carriage assessment and blood samples for antibody titration.
Main Results:
- Children aged 3.6 years had a geometric mean titre (GMT) of 1.06 µg/ml; by 4.5 years, GMT was 0.89 µg/ml.
- Eight percent of children with undetectable antibodies responded robustly to a booster dose.
- Children exposed to Hib showed higher GMTs compared to unexposed children.
Conclusions:
- Accelerated Hib immunization without a second-year booster provides satisfactory antibody concentrations until 4.5 years of age.
- Immunological memory is likely present in individuals with undetectable antibody levels.
- The findings support the efficacy of current accelerated infant vaccination schedules for Hib.
Objectives:
To assess the persistence of serum Haemophilus influenzae type b antibodies and the prevalence of H influenzae type b carriage in a group of preschool age children previously vaccinated in infancy.
Design:
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 fifty three children at a median age of 3.6 years had a geometric mean titre (GMT) of 1.06 micrograms/ml (95% CI 0.80 to 1.38). Eight per cent had an undetectable antibody concentration, received a booster dose of plain PRP vaccine, and responded with concentrations > 2 micrograms/ml. GMT at 4.5 years of age was 0.89 microgram/ml (0.69 to 1.16). Twelve children who had been exposed to H influenzae had a GMT of 4.7 v 0.8 micrograms/ml for those without exposure.
Conclusions:
Accelerated immunisation against H influenzae without a second year booster results in persistence of satisfactory serum concentrations of antibody to 4.5 years of age. In those with undetectable antibody, immunological memory may still be present.