Vaccination against rabies and protective antibodies - comparison of ELISA and fluorescent antibody virus neutralization (FAVN) assays

The aim of the study was monitoring the efficacy of primary vaccination against rabies and the need for booster doses. These studies validate at the same time recent technological improvements in laboratory diagnostics of the level of rabies protection in human sera. Research was carried out into the level of antibodies, considering that an antibody titer ≥0.5 IU/mL is protective. We used Platelia rabies ELISA kit (BIO-RAD Laboratories) for the detection of rabies virus anti-glycoprotein antibodies in 41 human sera of previously healthy veterinarian students. Neutralisation rabies virus antibodies were also measured simultaneously by fluorescent antibody virus neutralization (FAVN) test. Two to eight years prior to entering the study subjects had received rabies treatment with human diploid cell vaccine (HDCV, Rabivac, Chiron Germany) according to the schedule: one vaccine on days 0, 7, 21 and 365. Mean level of rabies antibody detected by ELISA was 19.6 (SD 18.8 minimum 1 maximum 56). Results were higher in the groups vaccinated recently. No subject had titer ≤0.5 IU/mL in ELISA, as well as in FAVN. In FAVN test the average titer was higher, reaching 54.4 (SD 44.3 minimum 0.7 maximum 152.5). An immune-complex-like reaction occurring after administration of the booster doses of rabies vaccine is the reason for reconsideration of the needs for administration of booster rabies vaccines. At the same time, the need for mass protection of professionals exposed subjects to rabies virus is real everywhere. Results of these studies indicate that HDCV is highly protective in both FAVN and ELISA tests. A high level of protection lasts at least 8 years in human sera. Average levels of detected rabies antibodies were lower in ELISA in comparison with FAVN test. A correlation between the two tests was found.