A single vaccination of commercial broilers does not reduce transmission of H5N1 highly pathogenic avian influenza

Table 1 Overview of HI titers at challenge, virus isolation data, clinical symptoms, and mortality rates

				Number of birds
		Mean HI titer (absolute (sd))		with HI titer ≥ 2^5 at challenge		shedding virus ^a		with clincial symptoms		that died
Exp.	Treatment	at challenge ( ² log)	at end ^d ( ² log)	I ^b	C ^b	I	C	I	C	I	C
1	no vaccination challenge at d28 of age	1.6 (1.0)	206 (457)	0	0	22	19	22	22	22	16
2	vaccination at d1 challenge at d28 of age	1.7 (1.3)	166 (381)	0	0	22	18	19	16	16	15
3	vaccination at d10 challenge at d28 of age	1.8 (0.9)	251 (357)	0	0	18	15	16	10	13	7
4	no vaccination challenge at day 1 of age	4.9 (1.2)^c	1.0 (0.4)^f	Nd^c	nd	16	6	19	19	13	1

^a total numbers in each group were 22 inoculated chickens and 22 contact-exposed chickens.
^b I: inoculated chickens; C: contact-exposed chickens.
^c not determined.
^d only from surviving and infected birds.
^e from surplus birds.
^f one bird had a titer of 1024, which is omitted from this average.