Cross-Protective Efficacy of Monovalent Live Influenza B Vaccines against Genetically Different Lineages of B/Victoria and B/Yamagata in Ferrets

Table 4

Virus replication in lungs and upper respiratory tract of ferrets, as measured by real-time PCR.

Group	Vaccination		Challenge
	Vaccine administered	Ct,^1 day 3	WT challenge virus given, day 21	Ct in nasal washes, day 24	Ct in lung tissue, day 24
1	B/Vic LAIV	11.41 ± 0.611^2	B/Vic WT virus	31.34 ± 4.663	negative
2	B/Vic LAIV		B/Yam WT virus	24.69 ± 1.462	negative
3	B/Yam LAIV	15.04 ± 0.806	B/Yam WT virus	negative	negative
4	B/Yam LAIV		B/Vic WT virus	19.46 ± 4.105	29.98 ± 0.950
5	None	n.d.^3	B/Vic WT virus	14.92 ± 2.142	29.18 ± 0.566
6	None	n.d.	B/Yam WT virus	17.89 ± 0.552	27.86 ± 0.167
7	None	negative	None	negative	negative

t: threshold cycle, the number of PCR cycles necessary to achieve a given level of fluorescence.
² Mean value ± standard error of mean. ³n.d.: not determined.