Table 1.

Potential targets for a universal influenza vaccine and their limitations.

Protein	Location	Site targetted	Function of target	Immune effector	Possible role in influenza protection	Escape possible
HA	Virion surface	HAI_ (head)	Virus binding	nAb	Block HA binding	Yes
	Virion and cell surface	HA2 (stem)	Viral fusion	Non-nAb	Block HA maturation, Fc-mediated lysis	No
NA	Virion surface	Sialidase	Virus release	Non-nAb	Block NA cleavage and virus release	Yes
M2	Infected cell surface	M2 Ectodomain	Ion channel	Non-nAb	Block virus entry	No
NP	Infected cell surface	Unknown	RNP structure	Non-nAb	ADCC and complement mediated lysis	Unknown
	Infected cell	Conserved pMHC	RNP structure	T cells (CD4+ and CD8+)	T cell cytotoxicity reduces viral load	Yes (limited)
All	Infected cell	Conserved pMHC	Various	T cells (CD4+ and CD8+)	T cell cytotoxicity reduces viral load	Yes (limited)