The unprecedented in recent history global COVID-19 pandemic urged the implementation of all existing vaccine platforms to ensure the availability of the vaccines against COVID-19 to every country in the world. Despite the multitude of high-quality papers describing clinical trials of different vaccine products, basic detailed data on general toxicity, reproductive toxicity, immunogenicity, protective efficacy and durability of immune response in animal models are scarce. Here, we developed a β-propiolactone-inactivated whole virion vaccine CoviVac and assessed its safety, protective efficacy, immunogenicity and stability of the immune response in rodents and non-human primates. The vaccine showed no signs of acute/chronic, reproductive, embryo- and fetotoxicity, or teratogenic effects, as well as no allergenic properties in studied animal species. The vaccine induced stable and robust humoral immune response both in form of specific anti-SARS-CoV-2 IgG and NAbs in mice, Syrian hamsters, and common marmosets. The NAb levels did not decrease significantly over the course of one year. The course of two immunizations protected Syrian hamsters from severe pneumonia upon intranasal challenge with the live virus. Robustness of the vaccine manufacturing process was demonstrated as well. These data encouraged further evaluation of CoviVac in clinical trials.

Currently the only effective measure against tick-borne encephalitis (TBE) is vaccination. Despite the high efficacy of approved vaccines against TBE, rare cases of vaccine failures are well documented. Both host- and virus-related factors can account for such failures. In this work, we studied the influence of mouse strain and sex and the effects of cyclophosphamide-induced immunosuppression on the efficacy of an inactivated TBE vaccine. We also investigated how an increased proportion of non-infectious particles in the challenge TBE virus would affect the protectivity of the vaccine. The vaccine efficacy was assessed by mortality, morbidity, levels of viral RNA in the brain of surviving mice, and neutralizing antibody (NAb) titers against the vaccine strain and the challenge virus. Two-dose vaccination protected most animals against TBE symptoms and death, and protectivity depended on strain and sex of mice. Immunosuppression decreased the vaccine efficacy in a dose-dependent manner and changed the vaccine-induced NAb spectrum. The vaccination protected mice against TBE virus neuroinvasion and persistence. However, viral RNA was detected in the brain of some asymptomatic animals at 21 and 42 dpi. Challenge with TBE virus enriched with non-infectious particles led to lower NAb titers in vaccinated mice after the challenge but did not affect the protective efficacy.

Вирус клещевого энцефалита (ВКЭ) является возбудителем тяжелого неврологического заболевания человека и широко распространен на территории Евразии. При репродукции флавивирусов помимо инфекционных вирионов накапливается набор неинфекционных вирусных структур: незрелые формы вирионов, пустые формы (не содержащие геном вирусные частицы), а также агрегаты поверхностного белка Е, способные оказывать влияние на иммунный ответ, и патогенез. Штаммы ВКЭ могут различаться по соотношению этих форм в инфекционном материале, т.е. по характеру структурной гетерогенности. Цель: подобрать комплекс методов, способных выявить данные различия. Методы. Общую концентрацию белка Е определяли методом ИФА, число частиц, содержащих геном (ГСЧ) - ПЦР в реальном времени, а для выявления инфекционных вирусных частиц - титрование в культуре клеток. Результаты. Разработан метод оценки структурной гетерогенности популяции ВКЭ. Было показано, что повышенное содержание неинфекционных вирусных частиц, содержащих геном, и несвязанных с ними белка Е не зависит от подтипа вируса. Выводы. Штаммы ВКЭ отличились по соотношению общего числа ГСЧ к числу инфекционных вирионов и по содержанию белка Е, связанного и несвязанного с ГСЧ. Tick-borne encephalitis virus (TBEV) is widespread in Europe and Asia and causes severe neurological disease in humans. It has been established that the reproduction of flaviviruses leads to the accumulation of a whole set of non-infectious viral structures aside from infectious virions. These structures include immature virions, empty forms (containing no genome) and aggregates of the surface protein E. These structures, despite being non-infectious, are able to influence the immune response and, consequently, the pathogenesis of TBEV infection. The aim of this work was to select a set of methods which can be implemented to identify these differences. Methods. Virus samples were analised for protein E concentration, number of genome-containing particles and infectivity. The total concentration of protein E in samples was evaluated using ELISA. The number of genome-containing particles was determined by a real-time PCR, and to assess the number of infectious virus particles titration in PEK cell culture was used. Results. An assay for total concentration of protein E in culture fluid of cells infected with different strains of TBEV based on the commertially available ELISA kit was developed. TBEV strains used in the study varied by the ratio of genome-containing particles to infectious virions. The amount of protein E not associated with genome-containing virions was calculated as a difference between total content of protein E and the amount of protein E bound to genome-containing particles. This amount was also different for studied samples of TBEV strains. Conclusion. No correlation was observed between the increased content of non-infectious genome-containing particles or the amount of residual protein E and TBEV subtypes.