Introduction. The emergence and spread of new genetic variants of SARS-CoV-2 underlies periodic upsurge in COVID-19 incidence. It has been shown that the most rapidly spreading genetic variants of SARS-CoV-2 are resistant to antibodies specific to the previous variant of the SARS-CoV-2, thereby necessitating to analyze the antibody evasion ability of previously circulating variants for newly emerging subvariants. The aim of this work was to assess SARS-CoV-2 cross-reactivity of coronavirus strains belonging to different genetic subvariants of Omicron isolated in the territory of the Russian Federation in the period 2020–2023 in microneutralization reaction using hyperimmune mouse sera. Materials and methods. Mouse hyperimmune sera were obtained against 10 SARS-CoV-2 strains belonging to subvariants BA.1, BA.2, CH.1.1, BN.1, BA.5.1, CL.1.2, BA.5.2, BQ.1.2.1 XBB.1.5 and XBB.3. BALB/c mice were immunized with inactivated concentrated antigen mixed at 1:1 ratio with an adjuvant representing Quillaja saponaria saponin-based virus-like immunostimulatory complex. The antibody titer was determined by neutralization test. The neutralizing activity of the hyperimmune sera was analyzed against the relevant viruses as well as against previous genetic variants of SARS-CoV-2 (Wuhan, Alpha, Beta, Gamma, Delta). Results. Cross-reactivity for all Omicron-variant strains analyzed here was shown; the degree of cross-reactivity depended on the degree of inter-strain relatedness. A prominent cross-reactivity was observed for subvariants of BA.5 so that their neutralizing activity against recombinant SARS-CoV-2 lineages was markedly reduced. Neutralizing serum titers obtained for subvariants of BA.5 against genetic variants of SARS-CoV-2 isolated during the early periods of the pandemic are reduced more than 60-fold. Conclusion. The presented method for obtaining and using hyperimmune mouse sera for neutralization reaction allows the assessment of cross-reactivity for strains belonging to different SARS-CoV-2 subvariants.
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