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http://www.medscape.com/viewarticle/447540

NEW YORK (Reuters Health) Jan 07 - Although immunization with a fourth Haemophilus influenza type b (Hib) vaccine does not increase antibody levels in preterm steroid-treated infants, it does appear to improve the avidity of the antibodies generated, according to a recent report.

The typical Hib vaccine schedule for term infants involves three injections in the first few months of life. Previous reports have shown, however, that this regimen may not achieve an adequate antibody response in preterm infants treated with steroids.

Dr. P. Clarke, from Hope Hospital in Salford, UK, and colleagues hypothesized that administration of a fourth vaccine may improve the antibody response of such infants. The researchers' findings are published in the January issue of the Archives of Disease in Childhood: Fetal and Neonatal Edition.

The study involved 12 infants born at less than 30 weeks gestation who had received dexamethasone for chronic lung disease. Six weeks after completing the standard Hib vaccine regimen, the infants received a fourth Hib dose.

The fourth immunization was not associated with a significant increase in anti-PRP antibody levels, the authors note. Moreover, infants who had subprotective antibody levels prior to the fourth dose continued to have subprotective levels after the extra dose.

Although the extra dose did not have a beneficial quantitative effect, it was associated with a qualitative improvement in Hib antibody. Specifically, PRP specific IgG avidity improved significantly after the fourth immunization.

Based on parental reports, administration of an extra dose was not associated with any adverse incidents, the investigators point out.

"An additional Hib dose given to recently steroid-treated preterm infants 6 weeks after the primary course does not appear to improve absolute titre of Hib antibody and cannot be currently recommended," the authors note. Still, "the avidity increase observed following the extra Hib dose suggests a qualitative improvement in antibody associated with boosting, and merits further investigation in a larger study."

Arch Dis Child Fetal Neonatal Ed 2003;88:F58-F61.

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