Different Australian subtypes of avian infectious bronchitis vaccines provide varying levels of cross-protection, which does not correlate with humoral antibody levels.
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Antibody levels should not guide IBV vaccine selection in poultry; leaves open optimal subtype strategies for broad cross-protection.
The cross-immunity of vaccinated chickens after challenge with some Australian infectious bronchitis viruses was assessed by humoral antibody responses and by ciliary activity in tracheal rings of vaccinated chickens following challenge. Four viruses were used for vaccination: Vac 3, Vac 4, both current infectious bronchitis vaccine viruses, and Q1/76 and N2/62. IBV N1/62 (synonym T0 and infectious bronchitis virus N9/74 (synonym Appin) were used to challenge the vaccinated chickens. Results showed a lack of correlation between humoral antibody levels and protection. Cross-immunity was found after vaccination with each subtype, but was lower for Vac 3 and Vac 4 than for Q1/76 and N2/62.
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ENDO‐MUNOZ et al. (1989) studied this question.
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