Attempts to Immunize Hamsters to West Nile Virus; Passive, Passive-Active and Active Methods.

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Abstract
Both passive-active and active methods of immunization of hamsters to West Nile (WN) virus were tried. The passive-active method gave very poor results; the active method gave satisfactory results. A procedure in which the hamsters are given 1 or 2 doses of 0.5 cc of freshly prepared WN vaccine, followed 1 week later by 100 hamster LD50 of WN virus, produced a satisfactory and rapid method of immunization. Hamsters immunized by vaccine plus active virus, when given large doses of cortisone and challenged with 108.5 LD50 of virus survived. These hamsters and similar immunized control animals not given cortisone had all failed to develop increased neutralizing antibody titers 3 weeks following the virus challenge. These results indicate that cortisone probably did not substantially reduce previously acquired immunity to disease or to infection.