NPM1 and influenza: Having established the utility of the co-culture ELISpot we used the technique to analyze influenza antigen specific responses in birds vaccinated (prime and boost) with recombinant Fowlpox (F9) or recombinant Fowlpox-NpM1 (F9-NpM1), and then challenged with an influenza virus with heterologous nucleoprotein and matrix protein.