Inactivated Newcastle disease vaccines: influence of virus concentration on the primary immune response

Inactivated vaccines of high potency could play a valuable role in Newcastle disease control programs. We determined the influence of virus concentration and method of concentration on the immune response of chidkens to inactivated vaccines. We used the LaSota strain of virus concentrated by either ultracentrifugation of polyethylene glycole precipitation. Virus concentration has a significant effect (P less than or equal to .01) on serum antibody levels at 2, 3, 4, and 6 weeks after vaccination; but during this same period, the antibody response was not significantly influenced by method of concentration. Virus concentration increased beyond 2000 hemagglutination units did not significantly increase (P greater than or equal to .05) the magnitude of the antibody response.