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Clinical and Vaccine Immunology, October 2007, p. 1328-1333, Vol. 14, No. 10
1071-412X/07/$08.00+0     doi:10.1128/CVI.00191-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Immunogenicity of a Fourth Dose of Haemophilus influenzae Type b (Hib) Conjugate Vaccine and Antibody Persistence in Young Children from the United Kingdom Who Were Primed with Acellular or Whole-Cell Pertussis Component-Containing Hib Combinations in Infancy

Immunisation Department, Centre for Infections, Health Protection Agency, London, United Kingdom,¹ Statistics, Modelling and Economics Department, Centre for Infections, Health Protection Agency, London, United Kingdom,² Gloucester Vaccine Evaluation Unit, Health Protection Agency, Gloucester, United Kingdom,³ Immunoassay Laboratory, Centre for Emergency Preparedness and Response, Health Protection Agency, Salisbury, United Kingdom,⁴ Vaccine and Immunisation Research Group, Murdoch Children's Research Institute and School of Population Health, University of Melbourne, Victoria, Australia,⁵ Immunoassay Laboratory, Institute of Child Health, London, United Kingdom⁶

Received 9 May 2007/ Returned for modification 10 July 2007/ Accepted 6 August 2007

In response to the rising incidence of Haemophilus influenzae type b (Hib) disease in the United Kingdom, a national campaign to give a booster dose of single-antigen Hib conjugate vaccine to children aged 6 months to 4 years was undertaken in 2003. Children (n = 386) eligible for Hib vaccine in the campaign were recruited. Hib antibody concentrations were measured before boost and at 1 month, 6 months, 1 year, and 2 years after boost and were analyzed according to children's ages at booster dose and whether a Hib combination vaccine containing acellular pertussis (aP) or whole-cell pertussis (wP) components was given in infancy. The geometric mean antibody concentrations (GMCs) before the booster declined as the time since primary immunization increased (P < 0.001), and GMCs were threefold higher in recipients of wP-Hib than aP-Hib combination vaccines (P < 0.001). GMCs 1 month after the booster increased with age (P < 0.001) as follows: 6 to 11 months; 30 µg/ml (95% confidence interval [CI], 22 to 40); 12 to 17 months, 68 µg/ml (95% CI, 38 to 124); and 2 to 4 years, 182 µg/ml (151 to 220), with no difference according to the type of priming vaccine received. Antibody levels declined after the booster, but 2 years later, GMCs were more than 1.0 µg/ml for all age groups. By extrapolating data for the decline in antibody levels, we found the GMCs 4 years after boosting were predicted to be 0.6, 1.4, and 2.6 µg/ml for those boosted at 6 to 11 months, 12 to 17 months, and 2 to 4 years, respectively, with levels of at least 0.15 µg/ml in about 90% of individuals. A booster dose of Hib vaccine given after the first year of life should provide long-lasting protection.

Published ahead of print on 15 August 2007.