Abstract
Korean government has selected and stocked five type antigens of two clades as Korean national antigen bank having high possibility of introduction to Korea. We aimed to evaluate the efficacy of the clade 2.3.2.1c and 2.3.4.4c H5Nx vaccines from the Korean avian influenza (AI) national antigen bank for emergency preparedness for their potency and protective efficacy against lethal homologous and heterologous viruses in layer and breeder chickens practically. The PD50 (dose of vaccine that protects 50% of chickens from viral challenge) of all vaccinated groups was >50, which was satisfied with minimum antigen requirement of OIE, and the PD50 levels of the two vaccines differed depending on strain and chicken breed. In homologous challenge, all vaccinated groups exhibited 100% survival with no clinical symptoms and high levels of pre-challenge protective immunity (7.2–8.5 log2), although they did not completely prevent virus shedding. On the other hand, against heterologous virus challenge, vaccinated animals exhibited 62.5–80% survival with lower antibody titers (2.3–3.4 log2) and a longer period of virus shedding (14 days post infection [dpi]). Our results suggest that the clade 2.3.2.1c and 2.3.4.4c H5Nx vaccines are good candidates for emergency vaccination of commercial chickens and support the idea that close genetic matching between vaccine and challenge virus provides the best protection.
Highlights
Korean government has selected and stocked five type antigens of two clades as Korean national antigen bank having high possibility of introduction to Korea
It is crucial that vaccine potency and efficacy are evaluated in commercial chickens prior to their emergency use in the field, because the efficacy of avian influenza (AI) vaccines differs among poultry species and breeds[19]
The minimum antigen requirement for licensing vaccines is 50 50% protective dose (PD50) per dose, which ensures that there is sufficient antigen mass or virus titer to be efficacious in the field[20,21]
Summary
We aimed to evaluate the efficacy of the clade 2.3.2.1c and 2.3.4.4c H5Nx vaccines from the Korean avian influenza (AI) national antigen bank for emergency preparedness for their potency and protective efficacy against lethal homologous and heterologous viruses in layer and breeder chickens practically. HPAI outbreaks of two subtypes (H5N6 and H5N8) were reported in 343 and 76 poultry farms in 2016 and 2017, respectively This period was associated with an unprecedented level of damage to the poultry industry in Korea: 38 million animals were culled, resulting in huge financial losses (approximately $312 million). We sought to evaluate the efficacy of the clade 2.3.2.1c and 2.3.4.4c vaccines from the Korean national AI antigen bank against homologous and heterologous HPAI viruses (HPAIV) in layer and breeder chickens
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