Article Text
Abstract
Objective: To describe the immune response of preterm infants, with a reduced response to primary Haemophilus influenzae type B (Hib) immunisation, to a fourth dose of Hib conjugate vaccine given in early life.
Design: Prospective observational study.
Setting: Five Wessex Neonatal Units.
Patients: Infants born at < 32 weeks and immunised with three doses of combined acellular pertussis-Hib vaccine, with a Hib IgG geometric mean concentration (GMC) < 1.0 μg/ml after these primary immunisations.
Interventions: An additional fourth dose of Hib conjugate vaccine given before 1 year of age. Blood taken to assess Hib IgG concentration and avidity after immunisation.
Main outcome measures: Hib IgG GMC and avidity index.
Results: Ninety six infants (mean gestational age at birth 29.1 weeks) received a fourth dose of Hib at a mean age of 7.8 months. Hib IgG GMC after the primary immunisations was 0.17 μg/ml (95% confidence interval (CI) 0.14 to 0.20) rising to 4.68 μg/ml (95% CI 3.36 to 6.57) after the fourth dose (p < 0.0001). The IgG response to the fourth dose correlated positively with the response after the primary immunisations (p < 0.001). Hib IgG geometric mean avidity index (GMAI) after the primary immunisations was 30.87 (95% CI 20.40 to 46.73). This increased to 124.73 (95% CI 109.93 to 141.51) after the fourth dose (p < 0.0001).
Conclusion: Preterm infants with very low IgG responses to Hib after primary immunisations with a combined acellular pertussis-Hib vaccine mount a good response to a fourth dose of Hib. This study suggests that all infants will benefit from a fourth dose of Hib, regardless of the age at which it is given.
- premature
- vaccines
- Haemophilus influenzae type b
- acellular pertussis
- booster
- 95% CI, 95% confidence intervals
- GMAI, geometric mean avidity index
- GMC, geometric mean concentration
- Hib, Haemophilus influenzae type B
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Footnotes
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Financial support: Department of Health; Meningitis Research Foundation