Field evaluations of pre-exposure use of human diploid cell rabies vaccine.

Following a case of human rabies in a Peace Corps volunteer (PCV) in Kenya in August 1983, ( 1) CDC, in cooperation with the Office of Medical Services, U.S. Peace Corps, con­ ducted serosurveys of 333 PCVs in eight countries to assess the adequacy of rabies pre­ exposure prophylaxis. Initial results indicate a lower-than-expected antibody response at several time periods following primary immunization. All PCVs had been immunized outside the United States between 1979 and 1983 using a three-dose regimen (days 0, 7, and 28) of 0.1 ml intradermal (ID) doses of human diploid cell rabies vaccine (HDCV) produced by the Merieux Institute (2 ). Serum specimens were collect­ ed by either CDC or the Peace Corps medical staff, and the rapid fluorescent focus inhibition test (RFFIT) for rabies-neutralizing antibody was performed at CDC on all specimens. Time from the initial immunization to sera collection ranged from 42 days to 2 years. PCVs serving in Kenya were most extensively studied. From September 1983 to October 1983, complete immunization histories and serum samples for rabies antibody determination were obtained from 90 of the approximately 25 0 PCVs in Kenya. Three cohorts were identi­ fied based on the time between primary immunization and collection of sera: (1) those immu­ nized 45 days before phlebotomy; (2) those immunized 10 -16 months before phlebotomy; (3) those immunized 2 years before phlebotomy. Serologic results for these groups were compared with results from previously published data at similar time periods after primary im­ munization (Table 1). Of the 25 specimens obtained 45 days after the beginning of primary immunization, only 17 (68%) were 0 .5 0 or more international units (IU)/ml, and five (20%) were lower than 1:16.* One of this group of 25 had no detectable antibody (< 1 :5 or < 0.05