Assessment of the safety and harmlessness of a recombinant candidate strain for the prevention of highly pathogenic H5N1 avian influenza

Within the framework of the Russian Science Foundation Grant No. 24-76-10044, a candidate vaccine strain of avian influenza virus A/Syktyvkar/PR8/6:2/HA20 (H5N1) was obtained, which has a low-virulent phenotype due to replacement of the hemagglutinin cleavage site. This virus does not cause the death of developing chicken embryos during incubation and the clinical manifestation of the disease in animals upon infection. The article presents the results of studies on the safety and harmlessness of a recombinant strain of avian influenza virus A/ Syktyvkar/PR8/6:2/HA20 (H5N1). No hemorrhages or lesions were observed in embryos infected with the live recombinant virus. The data obtained indicate the safety of the A/Syktyvkar/PR8/6:2/HA20 virus for embryonated chicken eggs. The study of harmlessness was carried out with intraperitoneal administration of an inactivated virus to white mice (this group also served as a control for inactivated drugs), and with the introduction of a virus inactivated with formalin, betapropiolactone and a mixture of theotropin and merthiolate. No significant weight loss was found in any of the observed groups, which indicates the harmlessness of the A/Syktyvkar/PR8/6:2/HA20strain for white outbred mice, as well as the good tolerability of drugs obtained using all the studied inactivation schemes. The harmlessness of an inactivated vaccine made from the inactivated virus strain with the addition of aluminum hydroxide as an adjuvant was tested by studying changes in the live weight of one-day-old Dekalb White cross chickens. In all study groups, there were no signs of exhaustion, intoxication, or signs of disease, which indicates complete inactivation and harmlessness of the virus. An assessment of the vaccine's harmlessness was also carried out on ten 150-day-old Dominant chickens. After a 10-fold inoculation dose was injected into the pectoral muscle, the birds were monitored for 28 days. All chickens remained alive during the specified time, with no visible clinical signs of illness, and there were no signs of an inflammatory reaction at the injection site. Thus, it can be concluded that the A/Syktyvkar/PR8/6:2/HA20 (H5N1) strain is safe, and inactivated vaccines made from this strain are completely harmless.

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