[Present situation of influenza vaccine development]

Influenza is a highly contagious acute respiratory disease, caused by influenza viruses infecting the host at the respiratory mucosa and repeated annually by appearance of variant viruses with altered surface antigens. To control influenza, a protective immunity must be provided in advance by administration with an inactivated or attenuated virus vaccine. Current inactivated vaccine, licensed for parenteral administration, can induce systemic IgG antibodies, but not highly cross-reactive mucosal IgA and heterosubtypic cytotoxic T lymdhocytes(CTL), to results in lowered protective efficacy against variant virus infection. Current attenuated virus vaccine, licensed for intranasal administration, can induce IgA and CTL, as well as IgG, with coryza, sore throat and febrile reactions and with forbidden use to high-risk patients. To improve shortcomings of the current inactivated or attenuated vaccine, many trials, including the development of DNA vaccine, are still going on.