The utility of real-time PCR as a test for confirmation of the absence of residual neurovirulence of strains for live antiviral vaccines

Introduction. Taking into account the particular importance of the assurance of the safety of antiviral vaccines containing, albeit attenuated, but live viruses, that can possibly retain the residual neurovirulence, it is important to develop additional tests to confirm the stability of attenuation using modern methods of laboratory diagnostics.The aim of the study was to assess the possibility of using the RT-PCR method as an additional test for monitoring the residual neurovirulence of attenuated rubella virus vaccine strains.Materials and methods. We used live attenuated vaccine strains of rubella virus "Orlov-V" and RA27/3. The study was carried out on 11 clinically healthy monkeys of the species Macaca mulatta weighing 3–5 kg, born and kept in the nursery of the Research Institute of Medical Primatology. The clinical material studied was tissue samples from various parts of the central nervous system (CNS), regional lymph nodes, parenchymal organs, plasma and cerebrospinal fluid of experimental animals. Control of extraneural dissemination of vaccine strains was carried out using virological (cytopathic action) and molecular biological methods (RT-PCR).Results. The absence of an infectious virus in the CNS, peripheral organs and blood plasma of monkeys infected with vaccine strains was demonstrated, which indicates a high level of attenuation of rubella virus strains "Orlov-B" and RA27/3. The analytical sensitivity of the RT-PCR method was found to exceed the analytical sensitivity of the cytopathic reaction by 1.7–3.3 lg when determining the content of rubella virus in the tissues of the CNS and peripheral organs of inoculated animals.Conclusion. Comparative analysis of experimental data showed that the detection of rubella virus by real-time PCR has a number of advantages due its specificity, sensitivity and a shorter turnaround time. In this connection, the RT-PCR method can be used as an additional test in the preclinical assessment of specific safety, namely, extraneural dissemination of attenuated vaccine strains, which is essential for quality and safety control of live rubella vaccines.