Endotoxin content in Haemophilus influenzae type b vaccine

Haemophilus influenzae type b (Hib) is a major cause of bacterial meningitis among children. Hib conjugate vaccines have effectively prevented Hib infection, and routine immunization with Hib conjugate vaccine has diminished the incidence of the disease in the United States and European countries. Introduction of Hib conjugate vaccines is also required in Japan. However, endotoxin that can carry over from Gram-negative H. influenzae with a purified component may contribute to adverse events following Hib vaccination. In the present study, we examined the endotoxin content in Hib conjugate vaccines. The Hib conjugate vaccine batches, which were produced by a European vaccine manufacturer, were shown to have considerably high endotoxin activity and to vary from 13.9 to 173.7 endotoxin units/dose. These results suggest that it is necessary to monitor the endotoxin content of the vaccine batches to ensure the quality and safety of the vaccines.