Improving the method of cultivation of respiratory syncytial virus to create a vaccine against respiratory infections of calves

The aim of the work was to study the features of cultivation and determination of the infectious activity of the respiratory syncytial virus strain "RB23" for the further creation of a live attenuated importsubstituting vaccine against IRT, PG-3 and RSV for nasal immunization of newborn calves. The quality of replication on cell lines was carried out by assessing infectious titers by the direct cytopathic effect of the virus on mammalian cells, and also using the stained foci method. The degree of RSV replication on the LEC cell culture depending on the cultivation time was determined by the quantitative PCR method. It was shown that LEC and T-1 cells are permissive for RSV. Moreover, the sensitivity of LEC cells exceeded the sensitivity of T-1 cells by 1.96, 1.88 and 7.69%, respectively, in three consecutive passages. Changing the MEM medium with the addition of glutamine during RSV cultivation on the 4th day contributed to an increase in replicative activity by 8.6% compared to flasks in which the medium was not changed. It was also noted that the optimal period for RSV cultivation is seven days, further cultivation leads to the degradation of extracellular viral particles, which reduces the concentration of virions by 26.5-40.0%. The RSV biomass "RB23" has been produced for further development of a live attenuated import-substituting vaccine against IRT, PG-3 and RSV for nasal immunization of newborn calves with an infectious RSV titer of 4.75±0.18 lg TCID ₅₀/cm³, a FFU titer of 1.5x10⁶ FFU/cm³ and a virion count in a virus-containing suspension of at least 4.5±0.20 million  copies/ml.

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