first appeared in China and has spread worldwide since then, including Korea. It is divided
into subclades ad, but the PR8-derived recombinant clade 2· 3· 4· 4 a viruses replicate
inefficiently in embryonated chicken eggs (ECEs). High virus titer in ECEs and no
mammalian pathogenicity are the most important prerequisites of efficacious and safer
vaccine strains against HPAI. In this study, we have synthesized hemagglutinin (HA) and …