Characterization of clade 2.3.4.4 highly pathogenic H5 avian influenza viruses in ducks and chickens

• Ducks are susceptible host of clade 2.3.4.4 H5 reassortant and the horizontal transmission among ducks were efficient.
• Clade 2.3.4.4 H5 reassortants were highly pathogenic in chickens.
• The current vaccines that are widely used in China may fail to confer protection against the H5 reassortants.

Worldwide dissemination of reassortant variants of H5 clade 2.3.4.4 highly pathogenic avian influenza (HPAI) viruses has posed a great threat to the poultry industry. Here, we systematically characterized the H5N2, H5N6 and H5N8 influenza viruses in poultry and compared them with those of previous clade 2.3.4 H5N1 virus. All the three H5 subtype reassortants caused systematic infection in ducks, and exhibited efficient direct transmission in ducks. All of them were highly pathogenic in chickens; however, the H5 reassortants have reduced virulence compared to the parental H5N1 virus. Antigenicity analysis revealed that the current vaccines that are widely used in China may fail to confer protection against the H5 reassortants.