The duration of immunity depends on the vaccination programme chosen. One of the most important
considerations affecting vaccination programmes is the level of maternal immunity in young chickens, which
may vary considerably from farm to farm, batch to batch, and among individual chickens. For this reason,
one of several strategies is employed. Either the birds are not vaccinated until 2–4 weeks of age when most
of them will be susceptible, or 1-day-old birds are vaccinated by conjunctival instillation or by the application
of a coarse spray. This will establish active infection in some birds that will persist until maternal immunity
has waned. Revaccination is then carried out 2–4 weeks later. Vaccination of fully susceptible 1-day-old
birds, even with live vaccines of the lowest virulence, may result in respiratory disease, especially if common
pathogenic bacteria are present in significant numbers.
The duration of immunity depends on the vaccination programme chosen. One of the most important
considerations affecting vaccination programmes is the level of maternal immunity in young chickens, which
may vary considerably from farm to farm, batch to batch, and among individual chickens. For this reason,
one of several strategies is employed. Either the birds are not vaccinated until 2–4 weeks of age when most
of them will be susceptible, or 1-day-old birds are vaccinated by conjunctival instillation or by the application
of a coarse spray. This will establish active infection in some birds that will persist until maternal immunity
has waned. Revaccination is then carried out 2–4 weeks later. Vaccination of fully susceptible 1-day-old
birds, even with live vaccines of the lowest virulence, may result in respiratory disease, especially if common
pathogenic bacteria are present in significant numbers.
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