The rTET-NA constructs derived from NAs across the two influenza A virus subtypes and two influenza B virus lineages present in the WHO recommended influenza vaccine composition for the 2018-2019 Northern hemisphere influenza season (A/Michigan/45/2015 N1; A/Singapore/INFIMH-16-0019/2016 N2; B/Colorado/06/2017 B/Victoria/2/87-like lineage; and B/Phuket/3073/2013 B/Yamagata/16/88-like lineage) were expressed in Chinese hamster ovary-S (CHO-S) cells and purified for further characterization. Here, XK is linked to influenza.