Abstract
Commercial specimens of desiccated chick-embryo-adapted living distemper vaccine were examined for virus content and divided into three classes, A, B and C. The LD50 values were 2.27 to 2.43 in class A vaccine, 1.25 to 1.58 in class Bvaccine, and less than zero in class C vaccine. These samples were injected into ferrets.
As a result, class A vaccine conferred power of defense against infection to the injected animals. Of six animals inoculated with class B vaccine, one died from infection. No protective power was given to animals injected with class C vaccine.
The power of producing neutralizing antibodies conferred to inoculated animals was in proportion to the virus content of the vaccine inoculated. Two specimens of vaccine prepared by different commercial laboratories had different power of producing such antibodies. No difference was observed, however, in the power of neutralizing different strains of virus among the vaccine specimens studied.
