Preclinical Studies of the Specific Activity of the Live Culture Vaccine VACD6 against Smallpox and other Orthopoxvirus Infections

Relevance. The epidemiological situation in the world is characterized by an increase in the incidence of orthopoxvirus infections in humans and animals. In this regard, it is necessary to develop new safe vaccines against these infections.

Aim. Conducting preclinical studies on the specific activity of the live vaccine against smallpox and other orthopoxvirus infections VACΔ6 based on the vaccinia virus (VACV) with six deleted virulence genes are presented.

Matherials and methods. The studies were performed in accordance with the requirements of the Guidelines for conducting preclinical studies of drugs (immunobiological preparations), the State Pharmacopoeia XIII and the European Pharmacopoeia 7.0.

Results and discussion. The vaccine strain VACΔ6 VACV showed significantly reduced neurovirulence in the model of intracerebral administration to suckling mice, and reduced inflammatorynecrotic activity in the model of intradermal administration to rabbits compared to the classical first­generation smallpox live vaccine approved for use in Russia. Preclinical studies of three series of the finished dosage form of the VAC∆6 vaccine showed its authenticity, thermal stability, non­pyrogenicity and safety. Double intradermal vaccination of rabbits at a dose of 10⁶ PFU/animal, a 100% protective effect was provided against the intranasal infection of rabbits with VACV strain HB­-92 at a dose of 1995 LD₅₀ and a double intradermal vaccination of mice at a dose of 10⁶ PFU/animal, full protection was provided against the intranasal infection of mice with ectromelia virus strain K1 at a dose of 56 LD₅₀.

Conclusion. Based on the conducted complex of studies, it can be concluded that the created vaccine of the fourth generation VACΔ6 is safer compared to the live smallpox vaccine of the first generation and is not inferior to it in immunogenic and protective properties.

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