Preterm infants have been shown to respond with lower antibody levels of protective anti-polyribisolribitolphosphate (PRP) to immunisation against Haemophilus influenzae type b (Hib) than term infants. This may be particularly relevant in the UK where fourth doses of Hib vaccine were not given until September 2006, and preterm infants were at increased risk of Hib disease. Other measures such as antibody avidity may give valuable information. …