Table 1.

Outcome of Challenge Infection for Virus Pairs Evaluated in the Study

Virus Pair	Ferrets Protected, Proportion, by Interval Between Primary Infection and Challenge, d						Control
	1	3	5	7	10	14
A(H1N1)pdm09 → B	1/3	2/3	1/3	2/3	0/3	0/3	0/3
B → A(H1N1)pdm09	0/3	0/3	0/3	0/3	0/3	0/3	0/3
B → A(H3N2)	0/3	1/3	0/3	0/3	0/3	0/3	0/6
A(H3N2) → B	ND	0/3	ND	ND	0/3	ND	0/3
A(H1N1)pdm09 → A(H3N2)	0/3	3/3	3/3	3/3	2/3	0/3	0/6
A(H3N2) → A(H1N1)pdm09	0/3	0/3	2/3	2/3	0/3	0/3	0/6

Data are no. of ferrets in which challenge infection was prevented from secondary challenge/no. evaluated.

Abbreviation: ND, not done.