Performance assessment and validation of a plaque reduction neutralization test (PRNT) in support to yellow fever diagnostic and vaccine clinical trials.

Yellow fever (YF) virus is a mosquito-borne virus belonging to the Flaviviridae family that circulates in tropical and subtropical areas of Africa and South America. Despite the availability of an effective vaccine, YF remains a threat to travelers, residents of endemic areas, and unvaccinated populations. YF vaccination and natural infection both induce the production of neutralizing antibodies. Serological diagnostic methods detecting YF virus-specific antibodies demonstrate high levels of cross-reactivities with other flaviviruses. To date, the plaque reduction neutralization test (PRNT) is the most specific serological test for the differentiation of flavivirus infections and is considered the reference method for detecting YF neutralizing antibodies and assessing the protective immune response following vaccination. In this study, we developed and validated a YF PRNT. We optimized different parameters including cell concentration and virus-serum neutralization time period and then assessed the intra- and inter-assay precisions, dilutability, specificity, and lower limit of quantification (LLOQ) using international standard YF serum, sera from vaccinees and human specimens collected through YF surveillance. The YF PRNT has shown good robustness and 100% of intra-assay precision, 95.6% of inter-assay precision, 100% of specificity, 100% of LLOQ, and 95.3% of dilutability. The test is, therefore, suitable for use in the YF diagnostic as well as evaluation of the YF vaccine neutralizing antibody response and risk assessment studies.