South Korea: updating the HPAI antigen at the National Antigen Bank
Since 2018, Korea has been building an avian influenza national antigen bank for emergency preparedness; this antigen bank is updated every 2 years. The ideal avian influenza vaccine provides the best protection against viruses that are antigenically close to field viruses. Therefore, vaccines stocks need to be updated continuously to prevent infections by novel HPAI viruses. To update the vaccine strains in the antigen bank, a reverse genetics technology was used to develop two vaccine candidates against avian influenza strains belonging to clades 2.3.2.1d and 2.3.4.4h, and then their immunogenicity and protective efficacy were evaluated in SPF chickens challenged with H5 viruses. Clade 2.3.2.1d or 2.3.4.4h viruses have not been detected in Korea; however, outbreaks have continued to occur in neighboring countries, meaning that there is the potential for introduction into Korea at any time. The two vaccine candidates, named rgCA2/2.3.2.1d and rgES3/2.3.4.4h, were highly immunogenic, with hemagglutination inhibition (HI) titers of 8.2–9.3 log2 against the vaccine strain, and 7.1–7.3 log2 against the lethal challenge viruses (in which the HA genes shared 97% and 95.4% homology with that of rgCA2/2.3.2.1d and rgES3/2.3.4.4h, respectively). A full dose of each vaccine candidate provided 100% protection against the challenge viruses, with a reduction in clinical symptoms and virus shedding.
Vaccination against HPAI is not allowed in South Korea. These results suggest that both vaccine candidates developed can be used to update the vaccine strains in the AI national antigen bank.
