Table 2.

In vivo characterization of CA04 backbone polymerase mutant viruses^a

Virus name	PB1-F2 protein expression	PB2 alteration at:		MLD50b (log10 TCID50)	Survivalc (%)
		aa 627	aa 701
Rg CA04	No	E	D	5.8	80
CA04 PB2627K	No	K	D	5.8	80
CA04 PB2701N	No	E	N	5.8	80
CA04 PB1-F2	Yes	E	D	≥6.0	100
CA04 PB2627K-701N	No	K	N	5.8	80
CA04 PB1-F2 PB2627K	Yes	K	D	5.7	70
CA04 PB1-F2 PB2701N	Yes	E	N	5.9	90
CA04 PB1-F2 PB2627K-701N	Yes	K	N	5.9	90

^aAbbreviations: aa, amino acid; MLD₅₀, 50% mouse lethal dose; TCID₅₀, 50% tissue culture infectious dose as determined in Madin-Darby canine kidney cells.

^bDetermined by inoculating groups of 10 mice with 10^5.5 TCID₅₀ of the respective mutant viruses.

^cSurvival was monitored daily for 13 days pi.