Inactivated Smallpox Vaccine: Immunogenicity of Inactivated Intracellular and Extracellular Vaccinia Virus

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Abstract
Summary Inactivated vaccines were prepared from cell-associated vaccinia virus liberated mechanically from sheep dermal pulp and cultures of infected chick cells and from naturally released ‘free’ or extracellular virus. The inactivated vaccines induced dermal immunity in rabbits and protected mice against intracerebral challenge. Antibody produced by rabbits in response to inactivated cell-associated virus neutralized cell-associated but not free virus. Antibody to inactivated ‘free’ virus neutralized neither, whereas antibody to live virus neutralized both types of virus and prevented secondary spread in vitro. Antigenic differences between cell-associated and ‘free’ virus were also indicated by gel precipitation but not by complement fixation or haemagglutination-inhibition tests on the sera.