The interaction of live vaccine and maternal antibody in protection against infectious bursal disease.

An experiment was performed to determine the results of the interaction of a mild infectious bursal disease vaccine and two different levels of maternal antibody in chicks, at various ages after hatching, as judged by protection against challenge with virulent infectious bursal disease virus. Maternal antibody of both high and low initial levels prevented effective vaccination at 1 and 14 days of age but by 28 days of age the vaccine was effective in birds of both initial antibody levels. Only the high initial level of antibody showed itself to be protective against all of the effects of challenge, while the low level, though it reduced or eliminated deaths, was unable to prevent bursal lesions and acted as a hindrance to vaccination. There was no evidence that vaccination significantly reduced the protective effects of maternal antibody.