XK and infection: NA mRNA + sFL (Y) vaccination provided cross-lineage protection against B/Malaysia/2004 (V) virus, by preventing weight loss while the groups of combination C-mRNA + sFL, sFL alone, and NA mRNA alone showed 10%–13% weight loss on day 5 post-infection (5 dpi) with B/Malaysia/2004 (Fig. 5B and C).