Protective antibody responses against A(H1N1)pdm09 primed by infection and recalled by intranasal vaccination

This study investigated the effects of preceding infection and administration of whole inactivated virus (WIV) vaccine on immune responses against influenza virus challenge. Preceding infection alone provided minimal reduction in virus titer following viral challenge. Single administration of intranasal or subcutaneous WIV vaccine alone failed to reduce virus titers and induce antibody responses. Subcutaneous administration of A/Narita/1/09 (A/NRT)-WIV after A/NRT infection provided complete protection against infection and yielded low nasal IgA and high serum IgG antibody responses. Subcutaneous administration of A/NRT-WIV after A/Puerto Rico/8/34 (A/PR8) infection provided no protection. Conversely, intranasal administration of A/NRT-WIV after A/NRT infection provided complete protection and high nasal IgA and serum IgG antibody responses. While, intranasal administration of A/NRT-WIV after A/PR8 infection provided moderate reduction in viral titer with moderate increases in nasal IgA antibodies. These results indicate that intranasal vaccination is superior to subcutaneous vaccination in inducing protective immune responses after preceding heterologous infection.