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Responses to a fourth dose of Haemophilus influenzae type B conjugate vaccine in early life
  1. M H Slack,
  2. D Schapira,
  3. R J Thwaites,
  4. M Burrage,
  5. J Southern,
  6. D Goldblatt,
  7. E Miller

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    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.

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