Duration of Immunity with Vectormune® ND on Layers

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Abstract

Immunity provided by Vectormune® ND was followed up to 72 weeks of age in commercial layers after single application at day-old or as part of vaccination regimes including conventional live and killed ND vaccines. Efficacy of the different vaccination programs was checked, from 3 to 72 weeks of age, by serology and challenges at regular intervals with a recent velogenic NDV isolate belonging to genotype VII. The effect of challenge on egg production at the peak of production was also tested. Assessment of protection was done based on the prevention of clinical signs including the effect on egg-production and reduction of challenge virus shedding via the oro-nasal and cloacal routes. Single vaccination with Vectormune® ND provided complete or almost complete (95% at 4 weeks of age and 100% at all later challenges) clinical protection from 4 weeks of age up to 72 weeks of age. The immunity induced was so strong that it was able to prevent fully egg-drop due to challenge. Challenge virus shedding was significantly reduced both by the oro-nasal and cloacal routes compared to the controls: 3-5 log10 reduction in oro-nasal shedding and very limited or non-detectable cloacal shedding (6-7 log10 reduction). This result indicates strong systemic immunity which could efficiently reduce or prevent NDV infection to become viraemic.

Co-application of conventional vaccines in a prime-boost vaccination program further reduced oro-nasal shedding.

Vectormune® ND induced antibody-response that was detectable both by HI test from 4 to 72 weeks of age, and by commercial ELISA from 6-10 to 72 weeks of age. Antibody titres induced by Vectormune® ND alone were significantly lower compared to the ones obtained in birds that received Vectormune® ND combined with live and killed ND vaccines.

Vectormune® ND vaccine virus could be detected by PCR from 2 to 74 weeks of age, verifying life-long persistence of vaccine virus in vaccinated birds and thereby ensuring strong and long lasting immunity to ND.

The possibility of optimally controlled mass application of Vectormune® ND in ovo or s.c. to day-old chicks at the hatchery in combination with live apathogenic ND vaccine and its characteristic to induce efficient, life-long immunity even when applied in face of maternally derived antibodies makes this type of ND vaccination program a good choice and a promising tool for the prevention of ND.

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