Serological response of chickens after vaccination and challenge. Hemagglutination inhibition (HI) assay titers in vaccinated chickens at the indicated times following vaccination and challenge with homologous and heterologous viruses. HI titers were assessed at 14 days post-vaccination (dpv), at 21 dpv, and at 14 days post-infection (dpi). Single (full) vaccine doses were administered. Vaccines were (A) rgKA435/18.104.22.168c and rgES2/22.214.171.124c in layer chickens, followed by challenge with homologous or heterologous virus, and (B) rgKA435/126.96.36.199c and rgES2/188.8.131.52c in breeder chickens, followed by challenge with homologous or heterologous virus. Individual data points are shown, along with means and standard errors.