Comparison of the safety and immunogenicity of commercial lentogenic Newcastle disease vaccine strains in layer chicks in Nepal

Newcastle disease (ND) continues to affect poultry flocks in Nepal despite routine vaccination, with outbreaks suggesting vaccine failure and interference from maternally derived antibodies (MDA). This study compared the safety and antibody response of three commercial lentogenic ND vaccine strains (HB1, F1, F) in layer chicks carrying MDA. Chicks were divided into vaccine, control, and baseline groups, with vaccines administered via the oculo-nasal-oral route at day 3. Vaccine safety was observed for 21 days, while vaccine efficacy and MDA levels were assessed by measuring antibody titers on days 1, 14, 21, and 28 using ELISA. Baseline MDA titers were high on day 1 but declined to negligible levels by day 28, with an estimated half-life of 6–7 days. All vaccines were safe, with no adverse effects even at tenfold dose. Significant differences in antibody response were observed among vaccine strains ( P < 0.001). HB1 induced a stronger response by day 14, while F1 and F produced weaker responses. By day 21, HB1 achieved protective titers in 90 % of birds, compared with 60 % for F1 and 30 % for F. These findings confirm that all tested vaccines are safe but differ in immunogenicity, with HB1 showing superior performance.