Primary humoral immune responses to formalin inactivated hemorrhagic fever with renal syndrome vaccine (Hantavax): consideration of active immunization in South Korea.

The efficacy of a formalin-inactivated hemorrhagic fever with renal syndrome (HFRS) vaccine and the effectiveness of a related vaccination program have not been previously evaluated. We measured the primary immune responses to Hantavax by plaque reduction neutralizing antibody test (PRNT), hemagglutination inhibition test (HAI), ELISA and high density particle agglutination test (HDPA) in order to confirm a possible biological efficacy through independent substantiation of experimental results and to compare the results with previous studies. Following two doses of primary vaccination, the seroconversion rate of PRNT and HAI antibody was 33.3% (10/30) [95% C.I. 17.3-52.5%] and 26.7% (8/30) [95% C.I. 12.3-45.9%], respectively. The correlation between PRNT and HAI antibody showed a statistical significance (r=0.58, p<0.01). The seroconversion rate of HDPA and ELISA were both 76.7% (23/30) [95% C.I. 57.7-90.1%], which correlated well with each other (r=0.58, p<0.01). In our study, Hantavax elicited low neutralizing antibody responses, at least in the volunteers samples that we tested. The vaccination program, including the vaccine itself, that has been adopted by the national immunization program to protect against HFRS in Korea should be re-evaluated and re-formulated to produce a higher protective immune response rate.