Broad IBV protection induced by a live IBV-NDV vaccine containing a Mass and Q1 strain

Five vaccination-challenge trials were performed with a live attenuated vaccine which includes an infectious bronchitis virus (IBV) Massachusetts strain (H120, GI-1), an IBV Q1 strain (BNF 28/86, GI-16), and a Newcastle disease virus (NDV) cloned strain. The efficacy of the vaccine was tested in maternally-derived antibody-positive (MDA+) commercial layers against challenge with IBV M41, 793B, D388(QX) or Q1 challenge virus. The efficacy of the vaccine was also tested in SPF layers against challenge with IBV M41, D388(QX) or Variant 2 challenge virus. The vaccine was applied at day of hatch, and all challenges were performed at 3 weeks of age. At 5 days post-challenge, the ciliary activity of tracheal explants was examined to determine the level of protection. The level of protection induced by the vaccine in commercial layers against IBV M41, 793B, D388(QX) and Q1 challenge was 91%, 94%, 73% and 84%, respectively. The level of protection in the SPF layers against IBV M41, D388(QX) and Var2 challenge was 89%, 69%, and 96%, respectively. In summary, vaccination with a live attenuated vaccine which includes an IBV Massachusetts strain (H120, GI-1) and an IBV Q1 strain (BNF 28/86, GI-16) provides a substantial level of protection against the homologous and most heterologous challenge viruses, which are representatives of the IBV strains circulating worldwide.