[Intranasal inactivated influenza vaccine]

Natural influenza virus infection is well known to be superior to parenteral inactivated vaccines, which induce serum IgG antibodies(Abs) alone, in inducing the broad-spectrum cross-protection against variant virus infection. Secretory IgA Abs, which provide cross-protection strongly against infection with variant viruses within the same subtype mainly in the upper respiratory tract, serum IgG Abs, which provide cross-protection weakly against infection with variant viruses mainly in the lower respiratory tract, and cytotoxic T lymphocytes, which provide cross-protection against infection with different subtype viruses and whose role is not always big in humans, are involved in the defence mechanisms induced by natural infection. The development of intranasal inactivated vaccine, capable of inducing both IgA and IgG Abs, is important to improve the efficacy of current inactivated vaccine.