Table 1.

Embryo vaccination with recombinant IBVs, analysis of hatch, clinical signs, serological responses and protection from virulent challenge

Virus	Hatch rate (%)	Mean ciliary activity posthatch (%)	Serological response (log2) ELISA	Protection (based on ciliary activity postchallenge)
				Day 5	Day 7
Beau-R	73	71	6.30	0	30
BeauR–M41(S)	82	77	7.05	80	100
CV1	18	5	10.5	100	100
Placebo	85	98	≤5.64	0	0

Fertile SFP eggs were inoculated with either a commercial vaccine (CV1; 10⁴ EID₅₀); the molecularly cloned Beaudette strain Beau-R (10⁶ EID₅₀); Beau-R in which the S protein gene had been replaced by that from the pathogenic M41 strain, to make BeauR–M41(S) (10⁶ EID₅₀); or a placebo. Hatch was assessed at 21.5 days of incubation. Ciliary activity was assessed in five birds at day 6 posthatch, serological responses by ELISA at 4 weeks posthatch. All birds were challenged with virulent M41 at 4 weeks posthatch and the ciliary activity determined at 5 and 7 days postchallenge by microscopic observation of tracheal rings. A high percentage of ciliary activity was indicative of protection.