Immune Response to Vaccination Against Argentine Hemorrhagic Fever in an Area Where Different Arenaviruses Coexist

Neutralizing antibody (NT Ab) titers to Candid #1 (C#1) vaccine against Argentine hemorrhagic fever were studied for 2 years post-vaccination in 330 volunteers, to assess whether the kinetics and/or magnitude of this immune response is modified by previous infection with the arena viruses Junin (JUN) and lymphocytic choriomeningitis (LCM). A total of 160 volunteers received C#1, distributed as follows: without detectable pre-infection with arenaviruses ( n = 54); with pre-existing antibodies to JUN ( n = 55); with pre-existing antibodies to LCM ( n = 51). The remaining 170 individuals received placebo. Levels of anti-JUN NT Ab displayed a trend in which titers increased with the virulence of the infecting strain, from C#1 ( = 49> ), through subclinical JUN infection ( = 229 ), vaccination following subclinical infection ( = 367 ) to JUN clinical infection ( =773 ). It was also found that the mean titer of NT Ab to C#1 did not vary significantly during 2 years of study and was: a) significantly lower than that elicited by wild strains of JUN, both clinical and subclinical infections ( p < 0.01); b) significantly increased the titers of pre-existing anti-JUN Ab ( p < 0.01); and c) was not modified by pre-existing anti-LCM Ab ( p > 0.05). These data indicate that the immune response to C#1 boosts pre-existing immunity to JUN virus and is not changed by previous experience with LCM virus.