A novel approach to poliovirus vaccine neurovirulence testing: development of an enhanced 4-level scoring system

The ongoing promotion and administration of vaccines play a critical role in the global effort to eradicate poliovirus. The Monkey Neurovirulence Test (MNVT) is an essential method for evaluating the neurovirulence of viruses in both the Oral Attenuated Live Poliovirus Vaccine (OPV) and the Sabin Inactivated Poliovirus Vaccine (sIPV) to ensure they meet required safety standards. The “4-level scoring method” recommended by the World Health Organization (WHO) has served as a key pathological evaluation criterion in this test. However, its lack of scoring granularity often leads to subjective interpretation discrepancies among evaluators, which compromises the consistency and reliability of the MNVT results. To address these limitations, we have mapped the primary neuronal nuclei in monkey tissue sections and analyzed viral-induced damage distribution. As a result, we developed an Enhanced 4-Level Scoring System (integrating precise anatomical mapping and quantitative lesion analysis), which minimizes evaluator bias and significantly improves scoring stability and consistency.