Immunogenicity and protective efficacy of clade 2.3.2.1c and clade 2.3.4.4c H5Nx avian influenza antigen bank vaccines in mice, Korea

The immunogenicity and protective efficacy of inactivated clade 2.3.2.1c (rgKA435) and clade 2.3.4.4c (rgES2) H5Nx vaccines, which are representatives of an avian influenza antigen bank in Korea, were examined in mice. Mice were vaccinated twice and then challenged with homologous virus. Hemagglutinin inhibition and serum neutralizing antibody titers in the rgES2-vaccinated group were higher (4.4 ± 1.7 and 10.8 ± 2.3 log₂, respectively) than those in the rgKA435-vaccinated group (2.8 ± 1.1 and 2.5 ± 0.9 log₂, respectively). rgES2 conferred 100% protection, with no morbidity, no severe body weight loss, and no virus replication in any of the tissues tested. By contrast, 80% of mice in the rgKA435 group survived. One mouse in this group died at 10 dpi. Virus titers in the lung and turbinate were 10^2.5–3.5 TCID₅₀/0.1 ml at 3–7 dpi and 10^1.5 TCID₅₀/0.1 ml at 3–5 dpi, respectively. In particular, the viral titer in the turbinate from the rgKA435 group at 3 dpi was significantly lower than that in the equivalent control group (p < 0.05). The data suggest that both of these antigen bank vaccines are promising candidates for further evaluation in humans.