Field studies led by Wageningen University have demonstrated the efficacy of two avian flu vaccines in reducing mortality in poultry infected with the HPAI virus, although additional experiments are required to draw accurate conclusions about the vaccines’ impact on virus transmission.

The field studies were commissioned by the Dutch Ministry of Agriculture, Fishery, Food Security, and Nature (WBVR) following laboratory studies using the two experimental vaccines. For the field studies, 1,800 layer hens on two commercial poultry farms were vaccinated in September 2023. The field trials will be completed in the third quarter of 2025.

The layers were vaccinated with one of the HVT-vector vaccines: VECTORMUNE® AI¹ or VAXXITEK HVT+IBD+H5.² A third group of chickens were administered the VAXXITEK HVT+IBD+H5 vaccine at day of hatch, as well as a booster vaccination at 12 weeks of age. The layers were infected with Highly Pathogenic Avian Influenza H5N1 (HPAI H5N1), which is currently impacting wild birds, domestic and commercial poultry, and dairy cattle worldwide in an ongoing outbreak.

A randomly selected segment of the vaccinated chickens is being brought to WBVR for transmission experiments on four separate occasions throughout the field studies. The chickens were first brought to WBVR eight weeks post-vaccination, at which point they were fully protected against HPAI H5N1. The second transmission was conducted at 24 weeks of age, when egg production is at its peak.

There were no clinical signs of avian flu infection in any of the vaccinated layers, and they experienced a significant reduction in mortality. Specifically, the non-boosted vaccinated chickens had a mortality rate of 10 percent, compared to a 100 percent mortality rate in non-vaccinated control groups. No mortality was observed in the vaccinated layers that received a booster.  

Additionally, all vaccinated chickens showed greatly reduced amounts of virus shedding through excrement.

Although the researchers found a significant reduction in mortality in vaccinated chickens, they stress that they cannot yet draw conclusions about protection against sustained transmission until additional data is gathered from the later stages of the field studies, which will enable more accurate quantification of transmission and predictions of protection over time. So far, the researchers have observed a wide range in levels of immunity among individual layers within the same vaccinated flock, which would influence transmission.

Researchers on the studies include Kim Bouwman-te Selle, Ph.D., Nancy Beerens, Ph.D., Evelien Germeraad, M.Sc., Ph.D. candidate, and Jose Gonzales Rojas, Ph.D. of Wageningen Bioveterinary Research; Christine Jansen, Ph.D. and Mart de Jong, Ph.D. of Wageningen University and Research; Marieke Augustijn-Schretlen, D.V.M, Tuen Fabri, D.V.M, and M. K. de Wit of Royal GD; Arjan Stegeman, D.V.M., Ph.D. and Francisca Velkers, Ph.D. of Utrecht University; and Sjaak de Wit, D.V.M, Ph.D., Dipl. E.C.P.V.S. of Royal GD and Utrecht University.

References 

1. K.M. Bouwman, C.A. Jansen, M.C.M. de Jong, et al. “Progress report: Transmission study testing HVT-H5 vaccine against highly pathogenic avian influenza (HPAI) H5N1 virus (clade 2.3.4.4b).” Wageningen Bioveterinary Research Publications. September 2024. DOI: 10.18174/669647.
2. K.M. Bouwman, C.A. Jansen, M.C.M. de Jong, et al. “Progress report: Transmission study testing HVT-H5 vaccine against highly pathogenic avian influenza (HPAI) H5N1 virus (clade 2.3.4.4b).” Wageningen Bioveterinary Research Publications. September 2024. DOI: 10.18174/670266.