In an initial study in specified pathogen free (SPF) chickens, a heterologous virus neutralizing (VN) antibody response to IBV variants Q1, Variant 2 (Var 2), D388/QX (D388), D274 and Arkansas (DPI) was observed using a vaccination programme incorporating two different live-attenuated
IBV vaccines, followed by boosting with an inactivated vaccine containing IBV Massachusetts (Mass) antigen. Therefore, a more detailed study was undertaken in SPF layer-type chickens primed with IBV Mass and 793B vaccines. The efficacy of single or repeated vaccination with a multivalent inactivated
vaccine containing IBV antigen was determined against challenge with five virulent IBVs: Mass (M41), 793B (4/91), D388, Q1 and Var 2. The parameters assessed were serological response, respiratory signs, egg production, post mortem abnormalities in the reproductive organs and abdomen,
and incidence of IBV antigen in kidneys. Increased VN titres were recorded against the five IBV challenge strains, with a significantly higher level of protection against drops in egg production following challenge. The difference between one or two vaccinations with inactivated vaccine was
not significant in terms of egg production. However, a significantly increased level of protection was seen in the lower percentage of hens with free yolk in the abdomen and/or peritonitis post challenge with IBV variants, D388, Q1 and Var 2 not included in the vaccination programme. A lower
incidence of acute, degenerated ovaries was found in groups given one injection of inactivated vaccine following live priming, and this was significantly lower than in groups given only live priming.
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