CD4 and influenza: Intranasal administration of this adjuvant‐free T4‐CoV‐Flu vaccine induces remarkable mucosal immunity against both respiratory pathogens, including high‐titer neutralizing antibodies and secretory IgA, lung‐resident CD4+/CD8+ T cells, diverse memory B cells, and complete protection against SARS‐CoV‐2 and influenza challenges.