Prior Infection of Chickens with H1N1 or H1N2 Avian Influenza Elicits Partial Heterologous Protection against

There is a critical need to have vaccines that can protect against emerging pandemic influenza viruses. Commonly used influenza vaccines are killed whole virus that protect against homologous and not heterologous virus. Using chickens we have explored the possibility of using live low pathogenic avian influenza (LPAI) A/goose/AB/223/2005 H1N1 or A/WBS/MB/ 325/2006 H1N2 to induce immunity against heterologous highly pathogenic avian influenza (HPAI) A/chicken/Vietnam/14/ 2005 H5N1. H1N1 and H1N2 replicated in chickens but did not cause clinical disease. Following infection, chickens developed nucleoprotein and H1 specific antibodies, and reduced H5N1 plaque size in vitro in the absence of H5 neutralizing antibodies at 21 days post infection (DPI). In addition, heterologous cell mediated immunity (CMI) was demonstrated by antigen-specific proliferation and IFN-c secretion in PBMCs re-stimulated with H5N1 antigen. Following H5N1 challenge of both pre-infected and naı̈ve controls chickens housed together, all naı̈ve chickens developed acute disease and died while H1N1 or H1N2 pre-infected chickens had reduced clinical disease and 70–80 % survived. H1N1 or H1N2 pre-infected chickens were also challenged with H5N1 and naı̈ve chickens placed in the same room one day later. All pre-infected birds were protected from H5N1 challenge but shed infectious virus to naı̈ve contact chickens. However, disease onset, severity and mortality was reduced and delayed in the naı̈ve contacts compared to directly inoculated naı̈ve controls. These results indicate that prior infection with LPAI virus can generate heterologous protection against HPAI H5N