The 2009 pandemic H1N1 virus induces anti-neuraminidase (NA) antibodies that cross-react with the NA of H5N1 viruses in ferrets

► We detected NA-specific antibodies in LAIV immunized ferrets by an NI assay. ► NA antibodies against 2009 pandemic H1N1 cross-reacted with the NA of H5N1. ► No cross-reactivity was detected between NAs of 2009 H1N1 and seasonal H1N1. ► Plaque size reduction and sequence analysis confirmed the NA cross-reactivity.