Table 4.

Results of the vaccination-challenge tests.

Groupa	Vaccination strain	Challenge strain	Morbidity	Mortality	Antibody responseb										Virus recoveryc
					Vaccinated					Challenged					4dd	8d	12d	16d
					4d	8d	12d	16d	20d	4d	8d	12d	16d	20d
1	H120	ck/CH/LGX/130530	0/10	0/10	0/10	1/10	6/10	10/10	10/10	10/10	10/10	10/10	10/10	10/10	9/10	5/10	2/10	0/10
2	LDT3-A	ck/CH/LGX/130530	0/10	0/10	0/10	1/10	5/10	9/10	10/10	10/10	10/10	10/10	10/10	10/10	1/10	0/10	0/10	0/10
3	H120	tl/CH/LDT3/03	10/10	2/10	0/10	1/10	5/10	10/10	10/10	10/10	8/8	8/8	8/8	8/8	10/10	8/8	1/8	0/8
4	–	tl/CH/LDT3/03	10/10	3/10	–	–	–	–	–	0/10	7/7	7/7	7/7	7/7	10/10	7/7	0/7	0/7
5	–	ck/CH/LGX/130530	2/10	0/10	–	–	–	–	–	0/10	9/10	10/10	10/10	10/10	10/10	10/10	3/10	0/10
6	–	–	0/10	0/10	0/10	0/10	0/10	0/10	0/10	0/10	0/10	0/10	0/10	0/10	0/10	0/10	0/10	0/10

^aOne-day-old birds in groups 1 and 3 were vaccinated with 10⁴ EID⁵⁰ of the H120 vaccine, while birds in group 2 were vaccinated with the LDT3-A vaccine. Twenty-day-old birds in groups 1, 2, and 5 were challenged with 10⁵ EID₅₀ of the ck/CH/LGX/130530 isolate, while birds in groups 3 and 4 were challenged with the IBV isolate tl/CH/LDT3/03. Birds in group 6 were not exposed to any viruses and served as negative controls.

^bNumber that seroconverted/number inoculated.

^cTwo procedures were used for virus recovery after challenge, as described previously (Zhang et al., 2015). First, embryos that were inoculated with individual nasopharyngeal swab samples were observed for lesions. Second, RT-PCR using a pair of oligonucleotide primers, N(−) and N(+), was conducted on RNA recovered from the allantoic fluid of the same eggs. The results from the two procedures were identical. Numbers indicate the number of birds that were positive for virus recovery/number challenged.

^dDays after challenge.