Presented at the Neonatal Society 2003 Autumn Meeting.
Slack M1, Thwaites R2, Schapira D3, Miller E4
1 Department of Neonatal Medicine, Princess Anne Hospital, Southampton, UK
2 Department of Paediatrics, St. Mary’s Hospital, Portsmouth, UK
3 Department of Paediatrics, Royal Hampshire County Hospital, Winchester, UK
4 HPA CDSC Immunisation Division, Colindale Avenue, London, UK
Purpose: Study One: To investigate the response of preterm infants with low levels of Haemophilus influenzae type b (Hib) IgG following primary immunisations to a fourth dose of Hib conjugate vaccine given in early life.
Study Two: To investigate the response of preterm infants to a combined diphtheria/tetanus/5 component acellular pertussis-Hib-inactivated polio vaccine, not previously used in the UK or in an accelerated schedule.
Study Design, Subjects and Procedures: Both studies were prospective and observational. Infants born at less than 32 weeks were recruited from 5 neonatal units in the Wessex region. Ethical approval was obtained from the four Local Research Ethics Committees serving the five centres.
Study One: Infants with Hib IgG <1.0mcg/ml after 3 doses of a DTaP-Hib vaccine (‘Infanrix-Hib’™, GlaxoSmithKline) given at 2/3/4 months received a fourth dose of Hib conjugate vaccine. Blood was taken 4 weeks after additional immunisation for Hib IgG assay at the Centre for Applied Microbiology and Research, Salisbury by enzyme linked immunosorbent assay (ELISA).
Study Two: Infants were immunized at 2/3/4 months with DT5aP-Hib-IPV (‘Pediacel’™, Aventis Pasteur MSD). Blood was taken 4 weeks after the third vaccine for Hib IgG assay.
Methods and Results: Study One: 96 infants (mean gestational age (MGA) at birth 29.1 weeks) had post-primary Hib IgG <1.0 mcg/ml and received a fourth Hib at mean age 7.8 months. Hib IgG Geometric Mean Concentration (GMC) post-primary immunisations was 0.17 mcg/ml (95% CI 0.14 – 0.20) rising to 4.68 mcg/ml (95% CI 3.36 – 6.57) post-fourth dose (p<0.0001). Hib IgG GM avidity index post-primary immunisations was 30.87 (95% CI: 20.40 – 46.73). This increased to 124.73 (95% CI: 109.93 – 141.51) post-fourth dose (p<0.0001).
Study Two: 45 infants (MGA 28.5 weeks) received 3 doses of a combined DT5aP-Hib-IPV vaccine at 2/3/4 months. Hib IgG GMC post-primary was 1.21 mcg/ml (95%CI 0.73-2.03mcg/ml) compared to 0.27 mcg/ml after 3 doses of ‘Infanrix-Hib’™, the previous UK vaccine (1) (p<0.0001). 80% of infants achieved a Hib IgG >0.15mcg/ml.
Conclusion: Preterm infants with very low IgG responses to Hib after primary immunisations mount a good response to a fourth dose of Hib. This suggests that all infants will benefit from an additional fourth dose of Hib, regardless of the age at which it is given. In addition, the DT5aP-Hib-IPV vaccine shows improved post-primary Hib responses in preterm infants compared to that seen with the previous vaccine.
References
1. Slack MH. J Infect Dis 2001;184:1617-20.