Comparison of RFFIT tests with different standard sera and testing procedures

Area of Science:

• Immunology
• Virology
• Public Health

Background:

• The World Health Organization (WHO) uses the rapid fluorescent focus inhibition test (RFFIT) to measure rabies antibody levels, indicating immunity post-vaccination.
• Standardized antibody testing is crucial for assessing vaccine efficacy and public health preparedness.

Purpose of the Study:

• To compare RFFIT results between the National Institute of Infectious Disease (NIID) in Japan and the Chinese Centre for Disease Control (CCDC).
• To evaluate the influence of different standard sera on RFFIT outcomes.
• To assess the consistency of RFFIT methodology across international laboratories.

Main Methods:

• Simultaneous RFFIT analysis was performed by both NIID and CCDC laboratories.
• Four serum samples (C1, S1, S2, S4) were tested in parallel using NIID's reference serum and the WHO standard serum.
• Neutralizing antibody titers were calculated using the standard formula.

Main Results:

• No significant differences were observed in the RFFIT methods employed by the NIID and CCDC, indicating good procedural consistency.
• Testing with NIID's tentative internal standard serum (TI-STD), adjusted to 2.0 IU of WHO standard serum, yielded higher antibody titers compared to using the WHO standard serum directly.
• The discrepancy in titers between the TI-STD and WHO standard serum suggests a potential variability in antibody quantification.

Conclusions:

• The RFFIT assay demonstrates reliable consistency between the NIID and CCDC laboratories for rabies antibody detection.
• A significant difference in detected antibody titers was observed when using a locally prepared standard serum versus the international WHO standard serum.
• Further investigation is warranted to understand the reasons for titer variations and to ensure accurate international comparability of rabies antibody measurements.