IMMUNIZATION OF MAN AGAINST EPIDEMIC TYPHUS BY INFECTION WITH AVIRULENT RICKETTSIA PROWAZEKI (STRAIN E)III. THE SEROLOGIC RESPONSE AND OCCURRENCE OF POST VACCINATION REACTIONS IN GROUPS VACCINATED UNDER FIELD CONDITIONS IN PERU12

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Abstract
After collection of pre-vaccination blood samples, 3135 persons of both sexes and all ages were inoculated with various doses of strain E vaccine or placebo by the intradermal, subcutaneous or intramuscular routes. The severity of immediate local and/or systemic reactions was directly related to size of inoculum, but not to age or pre-existing immunity, while severity of delayed reactions (9-14 days post-vaccination) showed the reverse relationship. Serologic response detectable by complement-fixation was elicited in more than 95% of the 543 persons non-immune prior to vaccination, regardless of size of dose, although the larger inocula generally provoked production of higher titers. Increase in CF titer occurred in 90% of 320 persons with detectable pre-vaccination CF antibody; no correlation existed between degree of elevation and size of inoculum or level of pre-vaccination CF titer. From the standpoint of post-vaccination reactions as well as serologic response, the intramuscular route was found to be the most satisfactory. No evident loss in potency of the lyophilized vaccine occurred after 8 months use in the field.