Effect of Vaccination Timing on Systemic Immunity against Newcastle Disease Virus in Broiler Chickens

Despite the extensive use of commercial vaccines, Newcastle disease virus (NDV) continues to be a significant hindrance to global poultry production. The failure of the vaccine, especially in areas with a predominance of genotype VII strains, is frequently reported, and in most instances, it is attributed to the interference of maternal antibodies and poor timing of the accompanying vaccination as opposed to the vaccine formulation. The current study assessed the impact of timing of vaccination on the humoral response, and the protective outcome of broiler chickens to virulent Newcastle disease virus (NDV). One-day-old Broiler chickens were randomly assigned into six groups, 30 per group. Each group was administered a Multi HN&F epitope mRNA vaccine (NDV) vaccine (constructed by the authors of the current study-data published in another paper), in which some received a booster at 1, 10, 5, or 15 days, while one group was unvaccinated and served as a control. On days 0, 14, and 28, serum samples were taken to measure and calculate antibody titers through Hemagglutination Inhibition (HI) and Enzyme Linked Immuno-Sorbent Assay (ELISA) tests. On day 28, intestinal and tracheal washes were completed to assess the production of IgA at the humoral immunity. On day 30, all groups were exposed to a Velogenic Newcastle Disease Virus (NDV) strain and were assessed for any clinical signs, mortality, and or survivability over a 14-day monitoring period. Vaccination at 10 days yielded a statistically significant increase in antibody titers (both HI and ELISA) in comparison to the early vaccinations. There was a noted decrease in humoral responsivity in the early vaccinated group when considering the washes from the tracheas and intestines. Day 10 vaccinations produced the highest concentrations of humoral Ig. Challenge survival rates were highest in the day-10 vaccination group (90%) and the double-vaccination group (93%), while the unvaccinated control group faced considerable mortality (15% survival). Vaccination timing influences systemic and humoral immunity to NDV. Optimizing antibody response and protection through delayed vaccination at day 10 represents an actionable approach to enhancing NDV control without the need to modify the vaccine.