Early Vaccination of Chickens Induces Suboptimal Immunity Against Infectious Bronchitis Virus

Area of Science:

• Veterinary Immunology
• Poultry Health
• Virology

Background:

• Infectious Bronchitis Virus (IBV) poses significant challenges in broiler chickens, despite widespread early-life vaccination.
• Current vaccination protocols often involve administering vaccines early post-hatch, but their impact on immune development requires further investigation.

Purpose of the Study:

• To evaluate the impact of prime vaccination age on systemic and mucosal immune responses to Infectious Bronchitis Virus (IBV).
• To assess the efficacy of booster vaccination in overcoming initial immune response differences.
• To investigate the effects of IBV vaccination on T-cell populations in broiler chickens.

Main Methods:

• Chickens were primed with an attenuated Arkansas (Ark) Delmarva Poultry Industry-type IBV vaccine at different ages, followed by booster vaccination.
• Systemic and mucosal antibody responses (IgA) were measured using ELISA.
• T-cell populations (CD4+, CD8+) were analyzed in immune effector sites and peripheral blood.

Main Results:

• Day 1 vaccination resulted in significantly lower antibody responses compared to later vaccination ages.
• Booster vaccination enhanced serum antibody levels, particularly when measured against Ark spike subunit 1 protein.
• Mucosal IgA levels decreased post-booster vaccination, while T-cell responses varied, with peripheral CD4+ cells showing increases in vaccinated birds.

Conclusions:

• Vaccinating broiler chickens on day 1 induces suboptimal immune responses, potentially contributing to viral persistence.
• Booster vaccination can mitigate initial immune response deficits, but may not fully restore mucosal immunity.
• Optimizing vaccination timing is critical for effective IBV control in poultry.