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Haemophilus influenzae type b (Hib) is a bacterial infection that causes meningitis in infants, especially in those below one year old. It is sometimes difficult to obtain good immune responses and protection in infants when using standard vaccines. Therefore, a new vaccine against Hib was developed in which a molecule from the bacteria was bound to tetanus toxin (Hib-TT). The safety and effectiveness of Hib-TT was evaluated in 77 healthy infants and in 10 infants receiving only diphtheria, tetanus, and whooping cough (DTP) vaccinations. Redness at the injection site, fever, or irritability were observed in under 15 percent of children. Protective levels of antibodies were found in 76 percent of children after the first injection, and this number increased after the second injection to 97 percent, while none of the control infants developed protective levels of anti-Hib antibodies. Among 66 children returning for follow-up at 18 months, 91 percent were still protected; the booster shot increased the number of children protected to 100 percent. Several types of antibody subclasses responded to the Hib-TT vaccinations, and the changes in levels of each are described. Antibodies against TT increased after the first, second, and fourth injections. The study suggests that vaccination with Hib-TT provides safe and effective protection against Hib infection, and does not interfere with immune protection against tetanus. (Consumer Summary produced by Reliance Medical Information, Inc.)