Table 2. Serologic testing of mice primed with different viruses.

Priming viruses	Serology Pre-challenge with Anhui/1(H7N9)
	Young mice					Aged mice c
	Against homologous virus		Against AH/1(H7N9)			Against homologous virus (HI)	Against AH/1(H7N9)(HI)
	HI a	MN b	HI	MN
Ck/HK/TP38(H9N2)	6.67 ± 0.82	4 ± 0.63	< 2	< 2		4.66 ± 0.48*	< 2
HK/33892(H9N2)	7 ± 0.5	6.4 ± 0.49	< 2	< 2		6.37 ± 0.48*	< 2
PR/8 (H1N1)	10.25 ± 0.43	8.8 ± 0.4	< 2	< 2		NA	< 2
CA/4 (H1N1)	9.44 ± 0.68	8.6 ± 0.49	< 2	< 2		8.33 ± 0.7*	< 2
Naïve mice	< 2	< 2	< 2	< 2		<4	< 2

^a Hemagglutination inhibition assay (HI) or ^b Microneutralization assay (MN) was performed on serum samples collected on d35 p.i; Log₂ of the HI or MN titers are expressed. Data represent mean ± SEM, n = 10–15/group.

^c Mice were primed at 16~18 months old.

* p<0.05, t test, aged versus HI titers in young group primed by the same virus.