Nontypeable Haemophilus influenzae: challenges in developing a vaccine.

Nontypeable Haemophilus influenzae (NTHi) is a gram-negative coccobacillus that is one of the bacteria that form the commensal flora of the upper respiratory tract in humans. This bacterium is an important human pathogen causing a broad spectrum of disease in both adults and children, including invasive and localised infections. The challenges in developing a bacterial protein antigen into an effective vaccine are, firstly, understanding what factors constitute an effective protective immune response for the host, and secondly, to design an effective delivery system that can target and induce the required immune response in humans that will prevent the variety of infections caused by NTHi.