Abstract
During the fifth month of 2024, many outbreaks of the avian influenza virus occurred in Vietnam, during which the first human infected with avian influenza A (H5N1) was reported. Therefore, influenza control strategies including vaccine production are necessary for poultry and improving the number of candidate vaccine viruses that do not replicate well in eggs for vaccine production. We previously reported that the ST-2009 virus had a negative propagation capacity in eggs. Chimeric neuraminidase (NA) genes were generated by replacing the 5' and 3' packaging signals of PR8 A/PR/8/34 strain with the coding region of the NA genes of ST-2009. Compared to those of the control, the new viruses containing chimeric NA genes exhibited significantly greater hemagglutination titers in embryonated chicken eggs. This study showed that the packaging efficiency of new viruses containing chimeric NA and replacing chimeric NAs improved the hemagglutination titer of viruses that were unable to propagate in eggs.