Vaccines are subject to specific regulatory requirements for the evaluation of their quality, safety, and efficacy. In 2005, the World Health Organisation (WHO), as the main international organisation coordinating measures to combat infectious disease outbreaks, began developing documents on the evaluation of vaccine quality, safety, and efficacy. The world’s leading regulatory authorities (FDA, EMA, etc.) have also issued recommendations for conducting non-clinical studies of vaccines.

The aim of this study was a critical review of the regulatory requirements established by foreign national and international regulatory authorities for non-clinical evaluation of the safety and efficacy of vaccines.

According to the study results, since the 2000s, the WHO and the world’s leading regulatory authorities have produced more than 40 regulatory documents describing certain aspects of non-clinical studies of the safety and efficacy of vaccines. These documents can be divided into two groups: the first group addresses non-clinical studies of vaccines in general, and the second one dwells upon the evaluation of the quality, safety, and efficacy of specific types of vaccines. For the Russian guidelines on non-clinical evaluation of the quality, safety, and efficacy of immunobiologicals, the latest revision dates back to 2013 and does not provide any information on new medicinal products. Currently, work is underway to prepare the regulatory framework for medicines, including vaccines, in the Member States of the Eurasian Economic Union (EAEU). This review of regulatory documents on non-clinical safety and efficacy studies of vaccines may be useful in drafting harmonised guidelines for the relevant groups of vaccines in the EAEU. It may also be of use to developers, manufacturers, and researchers involved in the creation and non-clinical study of vaccines.

In 1980, the World Health Assembly officially declared smallpox eradicated in the world, which allowed developed countries to stop preventive vaccination against this disease. However, circulating and emerging orthopoxviruses along with the lack of herd immunity prompt the need for emergency smallpox vaccines meeting the current requirements for biologicals.

The aim of the study was to analyse the safety and efficacy of third-generation smallpox vaccines based on the MVA strain of vaccinia virus compliant with the current (stricter) immunogenicity and safety requirements in healthy subjects and especially in patients with underlying health conditions, considering the lack of herd immunity to orthopoxviruses.

The authors analysed the existing experience with smallpox vaccines. The vaccines based on the modified vaccinia Ankara (MVA) strain hold a special place amongst other third-generation vaccines, as this strain is safe and can be used for creating vector vaccines. Bavarian Nordic produces the MVA-based vaccine under three brand names (Imvanex in the EU, Jynneos™ in the USA, and IMVAMUNE® in Canada). According to the results of MVA-based vaccine clinical trials in healthy volunteers and patients with various underlying conditions, the main mild adverse drug reactions (erythema, pain, pruritus, and swelling) were mostly registered at the injection site. The systemic adverse drug reactions included fatigue, headache, myalgia, and chills; several subjects developed upper respiratory tract infections, nausea, and gastroenteritis, which resolved spontaneously within a day. MVA-based vaccines did not cause any cardiac abnormalities, including myo- or pericarditis. Thus, the vaccines may be used in patients with eczema, atopic dermatitis, inflammatory skin conditions, HIV, tuberculosis, cardiac abnormalities, as well as in children, adolescents, and pregnant women. The optimal intradermal immunisation dose was 1×10⁸ TCID₅₀. Two injections at this dose induced a pronounced humoral and cell-mediated immune response comparable to that induced by one administration of a first-generation smallpox vaccine. At this dose, the study vaccine also boosted pre-existing immunity conferred by a first-generation vaccine. The US Centers for Disease Control and Prevention recommend Jynneos™ for preventing monkeypox in adults (18 years of age and older).

Chikungunya fever is an acute infectious disease caused by the mosquito-borne Chikungunya virus (CHIKV). In the last decades, cases of the disease have been reported in more than 100 countries; therefore, CHIKV presents a global public health problem. CHIKV genotypes have limited antigenic diversity, and documented reinfection is very rare. Hence, a vaccine could prevent infection and potential disability, as well as reduce the epidemic spread of CHIKV in the population.

The aim of the study was to review approaches to the development of preventive vaccines against CHIKV, evaluate promising vaccine candidates in preclinical or clinical development stages, and analyse perspectives and challenges of bringing these vaccines to the pharmaceutical market.

According to the literature reviewed, both traditional and modern platforms are used in the development of CHIKV vaccines, which has been ongoing for several decades. Each platform has its advantages and limitations. The most popular platforms are live attenuated vaccines and vaccines with viral vector constructs. To date, about 25 vaccine candidates have successfully passed through preclinical studies, and more than 7 vaccine candidates have progressed to various phases of clinical studies. The preventive medicinal products that have reached the clinical development stage include 4 live attenuated vaccines, 1 inactivated vaccine, 1 vaccine containing virus-like particles, and 1 mRNA vaccine. All 7 candidates have demonstrated cross-protection against multiple genotypes of CHIKV at the level of either preclinical in vivo studies and/or clinical in vitro studies. The research continues, and this shows that not only the scientific community but also health systems are interested in bringing effective CHIKV vaccines to the pharmaceutical market.

Preventive vaccination against SARS-CoV-2 infection is currently receiving close attention in the Russian Federation. Improving public confidence in immunisation with new vaccines largely depends on a guarantee of the absence of side effects caused by contamination. A high risk of contamination is inherent to biological products, including coronavirus prevention vaccines, due to their properties and the nature of raw materials used. This risk adds to the need for using effective contaminant detection approaches.

The aim of the study was to evaluate the possibility to improve sterility testing of preventive vaccines against SARS-CoV-2 infection.

This article presents an analysis of the procedures proposed by pharmaceutical developers for sterility testing of ten Russian vaccines approved in the country for COVID-19 prevention. The authors considered specific characteristics of these vaccines, including their physical and chemical properties, the presence of antimicrobial components, and other critical factors affecting the correctness of the experimental setup. The results suggest that it is possible to improve sterility testing. According to the authors, the main directions for its improvement are the proposal to develop an alternative procedure based on compendial method 2 (OFS.1.2.4.0003.15, Ph. Rus. XIV), as well as the use of a universal culture medium. If used for refining the established procedures and developing new ones, the authors’ recommendations will improve the reliability and applicability of sterility testing during both manufacturing and pre-approval regulatory assessment of updated coronavirus vaccines for subsequent release to the market. The proposed approaches can be applied to testing other medicinal products for sterility.

Monitoring of the proportion of immune individuals and the effectiveness of vaccination in a population involves evaluation of several important parameters, including the level of virus-neutralising antibodies. In order to combat the COVID-19 pandemic, it is essential to develop approaches to detecting SARS-CoV-2 neutralising antibodies by safe, simple and rapid methods that do not require live viruses. To develop a test system for enzyme-linked immunosorbent assay (ELISA) that detects potential neutralising antibodies, it is necessary to obtain a highly purified recombinant receptor-binding domain (RBD) of the spike (S) protein with high avidity for specific antibodies.

The aim of the study was to obtain and characterise a SARS-CoV-2 S-protein RBD homodimer and a recombinant RBD-expressing cell line, as well as to create an ELISA system for detecting potential neutralising antibodies.

Materials and methods: the genetic construct was designed in silico. To generate a stable producer cell line, the authors transfected CHO-S cells, subjected them to antibiotic pressure, and selected the optimal clone. To isolate monomeric and homodimeric RBD forms, the authors purified the recombinant RBD by chromatographic methods. Further, they analysed the activity of the RBD forms by Western blotting, bio-layer interferometry, and indirect ELISA. The analysis involved mono clonal antibodies GamXRH19, GamP2C5, and h6g3, as well as serum samples from volunteers vaccinated with Gam-COVID-Vac (Sputnik V) and unvaccinated ones.

Results: the authors produced the CHO-S cell line for stable expression of the recombinant SARS-CoV-2 S-protein RBD. The study demonstrated the recombinant RBD’s ability to homodimerise after fed-batch cultivation of the cell line for more than 7 days due to the presence of unpaired cysteines. The purified recombinant RBD yield from culture broth was 30–50 mg/L. Monomeric and homodimeric RBD forms were separated using gel-filtration chromatography and characterised by their ability to interact with specific monoclonal antibodies, as well as with serum samples from vaccinated volunteers. The homodimeric recombinant RBD showed increased avidity for both monoclonal and immune sera antibodies.

Conclusions: the homodimeric recombinant RBD may be more preferable for the analysis of levels of antibodies to the receptor-binding domain of the SARS-CoV-2 S protein.

West Nile fever is a vector-borne zoonotic arbovirus infection with natural foci. Its clinical course is similar to that of acute febrile syndrome, and severe cases may result in neuroinvasive disease. Several genetic lineages (1, 2, and 4) of the West Nile virus (WNV) with different pathogenicity for humans are circulating in the Russian Federation. Therefore, it is an urgent task to develop a diagnostic reagent kit for differentiating between WNV genetic lineages and to implement the kit in clinical laboratory practice.

The aim of the study was to conduct technical and clinical tests and evaluate the quality, efficacy, and safety of the Ampligen-WNV-genotype-1/2/4 diagnostic reagent kit for detecting WNV RNA and differentiating between WNV genetic lineages 1, 2, and 4 by reverse transcription polymerase chain reaction (RT-PCR) with fluorescent probe-based detection.

Materials and methods. The authors determined the diagnostic sensitivity and specificity of the Ampligen-WNV-genotype-1/2/4 reagent kit (Volgograd Research Institute for Plague Control, Russia) by real-time RT-PCR with 216 clinical samples and 204 biological samples. Sanger sequencing was used as a reference method. Statistical analysis of clinical test results was carried out in accordance with the Russian national standard for clinical laboratory tests (GOST R 53022.3-2008).

Results. When tested with the Ampligen-WNV-genotype-1/2/4 reagent kit, real-time RT-PCR demonstrated the analytical sensitivity of 1×10⁴  GEq/mL for the detection of WNV cDNA of genetic lineages 1, 2, and 4. The assessment of its analytical specificity showed no positive results for cDNA samples of heterologous viruses at a concentration of 1×10⁶  GEq/mL. The diagnostic sensitivity with the reagent kit was at least 98.5%, and the diagnostic specificity was at least 99%, with 90% confidence levels for both parameters.

Conclusions. The Ampligen-WNV-genotype-1/2/4 reagent kit can be recommended for use in clinical laboratory diagnostics to detect WNV RNA and differentiate between WNV genetic lineages 1, 2, and 4.

The increase in the number of cell cultures for virology and biotechnology enhances the chances of a successful response to threats related to outbreaks of well-known and new human infectious diseases. It is a vital task to search for cell cultures sensitive to a wide spectrum of viruses.

The aim of the study was to investigate the sensitivity of new diploid animal cell cultures (fibroblasts of a foetal pig’s kidneys and larynx) to Coxsackievirus B5 (CVB5) and Herpes simplex virus-1 (HSV-1).

Materials and methods. The cultures of porcine foetal kidney fibroblasts (PFKF) and porcine foetal larynx fibroblasts (PFLF) were derived from a foetus of a healthy pig by mild trypsinisation. The study determined the sensitivity of these new PFKF and PFLF cultures to the above-mentioned viruses by the cytopathic effect (CPE) expressed as a percentage. The infectious activity of CVB5 was studied using real-time polymerase chain reaction (PCR) with the determination of amplification cycle threshold values (C_t); that of HSV-1 was studied using quantitative titration of the virus-containing liquid (VCL). Infectious activity values were expressed as tissue culture 50% infective doses (TCID₅₀).

Results. The authors developed diploid PFKF and PFLF cell cultures. PFKF cells demonstrated high sensitivity to CVB5, with a CPE of 87.5±3.3% after passage 3 and a satisfactory concentration of enterovirus RNA in the VCL of 22–24 C_t . The sensitivity of PFKF cells to HSV-1 corresponded to a CPE of 92.1±5.5%. In these cells, the infectious activity of HSV-1 corresponded to 10^4.25 TCID₅₀/0.2 mL. The experiments with PFLF cells showed low CPE and infectious activity values for both viruses.

Conclusions. The study demonstrated high CPE values with the CVB5 (CB5-8100) and HSV-1 (HSV-1/L-2) strains as examples and confirmed the sensitivity of the new diploid PFKF cell culture to these test viruses. Thus, the PFKF cell culture offers potential applications in virology and biotechnology and may be a candidate for testing other strains of CVB5 and HSV-1.

An increase in cases of chikungunya fever is reported in the Caribbean, Central and South America, and Southeast Asia. As there is no specific treatment for this disease and the only available treatment is symptomatic, it is very relevant to develop vaccines against chikungunya fever. To develop an inactivated whole-virion vaccine against the disease, it is important to choose a susceptible cell culture that both provides high virus yields and is used for vaccine production.

The aim of the study was to evaluate the susceptibility of multiple cell lines to Chikungunya virus infection and to select the monolayer culture method with the highest virus accumulation and yield.

Materials and methods. The study used the CHIKV_Nic strain of the Chikungunya virus and cell lines C6/36 (for virus titration), CEF, MRC-5, Vero, and 4647. While choosing the culture method, the authors used culture flasks, a cell factory, and roller bottles. The authors determined the susceptibility of the cell lines to viral infection by the degree of accumulation of the infectious agent in the culture fluid. The results of virus titration were calculated on day 5 on the basis of a pronounced viral cytopathic effect.

Results. The Vero and 4647 cell lines demonstrated the highest susceptibility to infection and virus concentrations in the culture fluid. The СEF and MRC-5 cell lines accumulated the virus at lower concentrations. The maximum virus titres (7.10–7.75 log₁₀ TCID₅₀/mL) were observed in the culture fluid 48 h after infection. The optimal multiplicity of infection (MOI) ranged between 0.001 and 0.0001 MOI/cell. At 0.0001 MOI/cell, the virus accumulated in the Vero cells cultured in roller bottles on day 2, with the maximum virus titre being 8.6±0.2 log₁₀ TCID₅₀/mL.

Conclusions. Vero cells meet the safety and stability requirements set for the production of chikungunya vaccines. The study determined the minimum MOI of the Chikungunya virus for cell culture. The roller bottle culture method provides the highest cell culture yield and the highest titre of the virus in the culture fluid.