Next, reverse genetics was used to create two viruses, one had the NA gene replaced with the gene for green florescent protein (GFP) with the conserved non-coding flanking base pairs (NCFBP) before and after (NCFBP-GFP-NCFBP) and another in which the GFP was flanked by NCFBP and the NA gene (NCFBP-NA-GFP-NA-NCFBP).