Bacterial otitis media: current vaccine development strategies.

Otitis media is the most common reason for children less than 5 years of age to visit a medical practitioner. Whilst the disease rarely results in death, there is significant associated morbidity. The most common complication is loss of hearing at a critical stage of the development of speech, language and cognitive abilities in children. The cause and pathogenesis of otitis media is multifactorial. Among the contributing factors, the single most important are viral and bacterial infections. Infection with respiratory syncytial virus, influenza viruses, para-influenza viruses, enteroviruses and adenovirus are most commonly associated with acute and chronic otitis media. Streptococcus pneumoniae, non-typeable Haemophilus influenzae and Moraxella catarrhalis are the most commonly isolated bacteria from the middle ears of children with otitis media. Treatment of otitis media has largely relied on the administration of antimicrobials and surgical intervention. However, attention has recently focused on the development of a vaccine. For a vaccine to be effective against bacterial otitis media, it must, at the very least, contain antigens that induce a protective immune response in the middle ear against the three most common infecting bacteria. Whilst over the past decade there has been significant progress in the development of vaccines against invasive S. pneumoniae disease, these vaccines are less efficacious for otitis media. The search for candidate vaccine antigens for non-typeable H. influenzae are well advanced whilst less progress has been made for M. catarrhalis. No human studies have been conducted for non-typeable H. influenzae or M. catarrhalis and the concept of a tribacterial vaccine remains to be tested in animal models. Only when vaccine antigens are determined and an understanding of the immune responses induced in the middle ear by infection and immunization is gained will the formulation of a tribacterial vaccine against otitis media be possible.