An increasing number of
infections of highly pathogenic
avian influenza virus (H5N1) in humans has been reported in South-East Asia and other areas of the world. High mortality (>60%) of this
viral infection and its pathosis of systemic
infection are features of this new human disease. Moreover, there is great concern that this avian H5N1 virus could cause a pandemic of new
influenza in humans, once it acquires the ability for human to human transmission. To prevent such highly contagious
infectious diseases as
influenza, it is essential to prepare effective
vaccines. Especially in the case of new influenza virus, we cannot predict the strain which will cause the pandemic. In such a situation, a
vaccine that induces cross-protective immunity against variant viruses is extremely important. However currently used parenteral seasonal
influenza vaccine is strain-specific, and is less effective against variant viruses. In order to overcome the weakness of current
vaccines we need to learn from the immune responses induced by natural
infection with influenza viruses. In the case of mucosally acquired acute respiratory
infection such as
influenza, mucosal immunity induced by natural
infection plays important role in protection against the
infection, as mucosal
secretory IgA antibody plays an important role in cross-protection. In this review we describe the advantages and development of mucosal
vaccine against highly pathogenic H5N1 influenza viruses.