The immunogenicity and efficacy of the vaccine is being evaluated in animal models. The serum antibody response to one or two doses of vaccine is being evaluated using hemagglutination inhibition and neutralizing antibody assays and T cell assays and the efficacy is being evaluated by challenging vaccinated animals with the wild-type H1N1 pandemic influenza virus. In collaboration with scientists from Singapore, we evaluated the efficacy of PIKA, a stabilized chemical analog of double-stranded ribonucleic acid, as prophylaxis against infection in mice with 5 different influenza A virus subtypes including the pandemic H1N1 virus. Intranasal treatment with PIKA resulted in significant reduction of viral replication in the respiratory tract. The inhibitory effect was mediated by rapid infiltration of immune cells into the lungs, and production of inflammatory cytokines. While TLR3 is important for the optimal production of these inflammatory cytokines, inhibition of viral replication was still observed in TLR3-/- mice. The broad-spectrum protection provided by PIKA makes it an attractive option for prophylaxis from infection with influenza A viruses. The influenza virus is constantly changing;immunity to one seasons strains does not translate into immunity in subsequent years. As a consequence, the vaccine is reformulated each year. The neutralizing antibody response to influenza virus is thought to be specific for a few antigenically related isolates within a given subtype. Heterosubtypic antibodies capable of neutralizing multiple subtypes have been recently isolated from phage libraries, but it was not known whether such antibodies are produced in the course of the immune response. In collaboration with scientists at the Institute for Research in Biomedicine in Switzerland, we found that following seasonal influenza vaccination, some individuals produced antibodies that cross-reacted with H5 hemagglutinin (HA). By immortalizing IgG+ B cells from four individuals we isolated a panel of 20 heterosubtypic monoclonal antibodies (mAbs) that bound and neutralized viruses belonging to several HA subtypes (H1, H2, H5, H6 and H9), including the recent pandemic H1N1 A/California/07/09 isolate. The mAbs used different VH genes and carried a high load of somatic mutations. With the exception of a mAb that mapped to the HA globular head, all heterosubtypic mAbs bound to acid sensitive epitopes in the HA stem region. Four mAbs were evaluated in vivo and protected mice from challenge with viruses representative of different subtypes. These findings reveal that seasonal influenza vaccination can induce a polyclonal heterosubtypic neutralizing antibody response that cross-reacts with the swine-origin 2009 pandemic H1N1 influenza virus and with the highly pathogenic H5N1 virus.