Infectious Diseases 2025

A field trial conducted at Wageningen University & Research (the Netherlands) evaluated the effectiveness of bird flu vaccines.
The two experimental bird flu vaccines under investigation in this field study provide long-term protection to layer hens but do not completely prevent mortality following infection. At the start of the trial in September 2023, 1,800 laying hens were vaccinated and housed on two commercial poultry farms. The study at these farms will continue until the third quarter of 2025.
During the trial, a subset of vaccinated chickens will be transferred to WBVR for a transmission study on four separate occasions. The first of these studies was conducted eight weeks post-vaccination, demonstrating that the hens were fully protected against bird flu at that age. The second study took place at 24 weeks of age, a period during which egg production reaches its peak.
Transmission
For the transmission study, a randomly selected group of chickens from the two commercial farms was transported to WBVR. The layer hens were vaccinated with one of two HVT-vector vaccines: VECTORMUNE® AI or VAXXITEK HVT+IBD+H5. Additionally, a third group was included, which received the VAXXITEK HVT+IBD+H5 vaccine at hatch and a booster vaccination at 12 weeks of age.
The animals were challenged with highly pathogenic avian influenza (HPAI) H5N1 virus (clade 2.3.4.4b). Transmission from inoculated to contact chickens was assessed, along with survival rates. Based on these data, the reproduction number (R) was estimated. Furthermore, virus shedding, as well as humoral and cellular immune responses, were analyzed.

Protection
In all vaccinated groups, no clinical signs were observed, and a significant reduction in mortality was noted compared to the non-vaccinated control groups. Mortality in the non-vaccinated control groups was 100%. In the groups that received a single vaccination, a mortality rate of 10% was observed. No mortality occurred in the group that received a booster vaccination.