Table 2.

Summary of emerging NA-based vaccine platforms against influenza viruses described in this review. + indicates low immunogenicity, +++ indicates high immunogenicity, N.D. indicates not determined. AA indicates amino acid.

Platform	NA Antigen Subtype	Animal Model	Immunogenicity	Protection	Ref.
Inactivated vaccine	30 AA insertion in seasonal N1 15 AA insertion in N2	Mice	+++ +++	N.D.	[96]
Recombinant NA vaccine	N2	Human	+	N.D.	[97]
	Seasonal N1 N2 B/Yamagata/16/88-like B-NA	Mice	+++ +++ +++	Homologous Heterologous	[27]
	Avian N1 Pandemic N1	Mice	+	Homologous Partial heterologous	[98]
	N1	Mice	+++	Homologous	[99]
	N2	Mice	+++	Homologous Partial heterologous	[100]
	B-NA	Mice Guinea pigs	+	Homologous Heterologous	[101]
	B-NA	Guinea pigs	+++	Homologous Partial heterologous	[102]
Virus like particles	Avian N1	Ferrets	+++	Homologous	[28]
	Pandemic N1	Mice	+	Homologous Heterologous	[103]
	Avian N1 Seasonal N1	Mice	+++	Homologous Heterologous	[104]
Viral replicon particles	Avian N1	Chicken	+++	N.D.	[105]
Viral Vector vaccines	Avian N1 Pandemic N1	Mice	+++	Homologous Heterologous Heterosubtypic	[106]
	N3 N9	Mice	+++	Homologous	[107]
Nucleic Acid-DNA	Seasonal N1	Mice	+	Homologous Partial heterologous	[108]
	N2	Mice	+	Homologous Partial heterologous	[109]
Nucleic Acid-RNA	Seasonal N1	Mice	+++	Homologous	[110]