An Attempt at Active Immunization with Plasmodium Vivax Killed in Vivo *

Abstract

It is now well known that convalescence from an untreated attack of vivax malaria is in part at least attributable to the acquirement of a very potent immunity to the strain of parasite which induced the attack, and we have shown (Boyd and Kitchen, 1943) that the level of immunity in such convalescents can be still further raised by a series of subsequent reinoculations with the homologous parasite. Indeed a level may be attained where the individual is able to withstand and promptly destroy doses of parasites many million times greater than the minimal number necessary to infect a fully susceptible person, and may with propriety then be regarded as hyperimmune. One of us has also discussed the criteria that may be used for the interpretation of the susceptibility status of persons naturally inoculated with vivax malaria (Boyd, 1942), with special reference to reactions indicative of homologous or heterologous immunity.