Influence of strain of chickens on the immune response to vaccination against Marek's disease.
Field trials were conducted to determine the response of different genetic strains of commercial chickens to vaccination against Marek's disease (MD). Cell-associated and cell-free HVT vaccines conferred the same degree of protection within the same strain of chickens. The incidence of MD in vaccinated birds seemed to be correlated with the natural susceptibility of the chicken strains to the disease. Revaccination did not induce better protection in the most susceptible strain.