Studies on infection and immunity in experimental typhoid fever. III. Effect of prophylactic immunization.

A study was made of the efficacy of various antityphoid immunizing agents in immunizing chimpanzees against typhoid fever produced by feeding viable S. typhosa. It was found that both acetone-killed and heat-killed, phenol-preserved typhoid vaccines were effective in protecting against infection induced with either homologous or heterologous strains of typhoid bacilli. Purified O antigen induced no discernible protection, but some immunity was afforded by the administration of purified Vi antigen.