Assessment of Immunological Interference Between Live Infectious Bursal Disease Virus and Avian Reovirus Vaccines in SPF Chickens

Infectious bursal disease virus (IBDV) and avian reovirus (ARV) are major immunosuppressive pathogens controlled through the widespread use of live attenuated vaccines. Concerns persist regarding potential immune interference when these vaccines are co-administered, though comprehensive in vivo data are lacking. Here, we reported the immunogenicity and protective efficacy of a live IBDV vaccine (W2512G-61) and a live ARV vaccine (ZJS) administered simultaneously or sequentially at 3-, 5-, and 7-day intervals in specific-pathogen-free (SPF) chickens. The IBDV live vaccine elicits strong, interval-independent humoral immunity and conferred 100% protection, demonstrating no compromise from ARV co-administration. Conversely, ARV-specific immunity was severely impaired by close temporal vaccination. ARV protection rates fell from 86.7% (ARV-only) to 46.7% with simultaneous administration and from 93.3% to 66.7% with a 3-day interval. Extending the interval to five or seven days eliminated this interference, restoring ARV antibody titers and protection to levels equivalent to ARV-only control vaccinated groups. This study provides the first definitive evidence of asymmetric immune interference between live IBDV and ARV vaccines. The results establish a minimum safe interval of five days to prevent interference and ensure robust ARV vaccine efficacy. These findings offer critical, evidence-based guidance for optimizing vaccination schedules to improve disease control in commercial poultry production.