Quantification of the neutralizing antibody titers (NAb) to KC and M41, respectively, by alpha NAb test (VNT) showed the neutralization index (NI) ≥1.5 in chicks immunized with rIBV-Beau-KC(S1), demonstrating that immunization of chicks with this recombinant virus could elicit comparable levels of cross-neutralizing antibodies against both KC and M41, with slightly higher titers against M41 than KC (Figure 5B). The gene discussed is CALCA; the disease is keratoconus.