This research focuses on analyzing the dynamics of neutralizing antibody (nAbs) titers against type 5 adenovirus (Ad5) in the adult population of Russia following vaccination against the novel coronavirus infection with recombinant adenovirus type-5 COVID-19 vaccine (CanSino Biologics, China). The impact of the Ad5 vector on nAb titers was investigated using 302 blood serum samples from individuals who received a single dose of the Ad5-nCoV vector vaccine. The research revealed that 33.8% of adults in Russia had pre-existing anti-Ad5 nAbs before the pandemic. Notably, 40% of vaccinated individuals did not exhibit an increase in nAbs titers upon receiving the Ad5-based vaccine. However, in the group with no or low titers of anti-Ad5 nAbs (1:10 -1:40), a significant 8-16-fold increase in nAb titers to Ad5 was observed.

Currently, the assessment of the immunogenic properties of influenza viruses as a part of influenza vaccines is carried out by using seroprotection, seroconversion as well as the rate of increases in post-vaccination antibodies. At the same time, significant differences in the immunogenicity of vaccines related to dynamic formation of high antibody titers responsible for long-term protection of the vaccinated, are neglected. Influenza viruses such as A(H1N1)pdm09 that caused 2009–2010 pandemic continue to circulate in the population, therefore, the assessment of the immunogenic activity of vaccine viruses prepared during the pandemic period is interesting in for the methodology to prepare pandemic vaccines to be used in various groups (adults, children, elderly people). Analyzing immunogenicity of influenza vaccines used during the 2009–2010 swine influenza pandemic and the post-pandemic period up to the year 2014 was carried out by applying the graphical method for assessing immunogenicity (immunographs) measured as follows: for each group of vaccinated subjects (depending on the vaccine used), an increased rate in antibody level was calculated and the graphs of immunogenicity were plotted. An increased rate of serum antibodies magnitude from vaccinated subjects and the number of sera (in %) with a given fold increase rate in antibody level from 1 to the maximum magnitude were plotted on the x- and y-axis, respectively. The proposed method for assessing immunogenicity allows to plot immunogenicity graphs regardless of the serum antibodies level found in volunteers. The assessment described above revealed a several features for developing immune response to the pandemic virus A(H1N1)pdm09 such as the lack of immune response in a substantial number of adult volunteers (25–27%) and young children (60–70%) after monovaccine administration. The reason for such immune response can be both an insufficient dose of vaccine-containing viral antigen and suppressed immune response caused by the influenza A(H1N1)pdm09. A study on the immunogenic properties for seasonal influenza vaccines containing the influenza A(H1N1)pdm09 virus antigen in the years 2010–2014 revealed a variety in emerging humoral immunity ranging from a short-term, low-frequency increase in antibodies from vaccinated children to the formation of high antibody titers in elderly. Practically, immunographic analysis of influenza vaccines particularly those derived from the influenza A(H1N1)pdm09 virus, may result in proposing recommendations to increase an antigenic load at the beginning of a pandemic cycle and/or block the suppressive properties of vaccine-contained viruses in pediatric vaccines, because escalating virus dose in the vaccine may not always be achievable in this case.

Antiepidemic measures were limited effectiveness for several years Objectives of this research were formulated as an assessment of the immunogenicity activity of the influenza virus A(H1N1)pdm09 in the composition of modern trivaccines Immunogenicity of the influenza virus A(H1N1)pdm09 in the vaccinated by vaccine was assessed by graphing, reflecting the dynamics of the multiplicity growth of antibodies (MG) and medium ratio of antibodies increasing (MR) in sera for several groups vaccinated. For comparison of vaccinated immunity was determined by traditional methods of evaluation of the immune response. As a result of the research, differences in the immunogenicity activity of the virus were revealed, which are reflected in antibody titers and the multiplicities of their growth from 2 to 4 - 8 times with the applying of similar quality vaccines. These changes couldn’t be observed with accounting study of the immune response. When immunized with a vaccine with an antigen dose of 5 mg HA identified a group of«silent» volunteers (8%) who did not respond to promotion with antigen A(H1N1)pdm09. Increasing dose of the influenza virus A(H1N1)pdm09 to 15 mg/dose in the split vaccine were result of the elimination of the group of«silent» volunteers. Simultaneously was observed a significant increase in the immune response in serum titers (up to 32-fold) and antibody growth rates Accordingly, using of the graphical form of accounting made it possible to better assess the details of the formation of collective immunity to the virus A(H1N1)pdm09 and the nature of its deviations in a number of cases.

An isotypic structure of system antibody response to influenza A(H1N1)pdm09 was analyzed in adult volunteers vaccinated with two inactivated monovalent subunit vaccines against pandemic influenza. The comparison group consisted of patients infected with influenza A(H1N1)pdm09 virus. In vaccinated volunteers the more active response of influenza-specific antibodies both with neutralizing properties (IgG1, IgG2, IgG3) and associated with allergic inflammation (IgG and IgE) was observed in comparison with infected patients. The high activity of the virus-specific serum IgA was observed both in infected patients and vaccinated volunteers. Antiviral hemagglutinating activity of antibodies in post-vaccination sera of vaccinated volunteers, unlike sera obtained from infected patients in the phase of recovery, were higher than protective level (1:40) according to HAI data.

The article discusses the results of study that demonstrated the possibility of successful application of radial hemolysis reaction in analyzing the human inoculation immunity to new strains of influenza virus serotype A A (H5N1) andA (H5N2). The radial hemolysis reaction provides accurate results on introduction of erythrocytes of horse or sheep into hemolytic system instead of erythrocytes of hens applied previously. The technique combines high sensitivity (in comparison with reactions of hemagglutination-inhibition and micro-neutralization, correlation coefficient 0.84-0.85) and total absence of inhibitors impact on the reaction results. During the investigation of immune response of patients who had pandemic virus A (H1N1) pdm09, radial hemolysis reaction demonstrated not only primary detection of antibodies to virus-agent (67°%) during pandemic, but also elective heightened sensibility in the zone of low titer serums (1:20) in hemagglutination-inhibition reaction. These characteristics are very important in analysis of antibodies levels at early stages of disease. The radial hemolysis reaction continues to be a reliable instrument in evaluating qualitative and quantitative indicators of humoral immunity in ill patients and persons inoculated with new strains of human influenza virus.

The article discusses the results of study that demonstrated the possibility of successful application of radial hemolysis reaction in analyzing the human inoculation immunity to new strains of influenza virus serotype A - A (H5N1) and A (H5N2). The radial hemolysis reaction provides accurate results on introduction of erythrocytes of horse or sheep into hemolytic system instead of erythrocytes of hens applied previously. The technique combines high sensitivity (in comparison with reactions of hemagglutination-inhibition and micro-neutralization, correlation coefficient 0.84-0.85) and total absence of inhibitors impact on the reaction results. During the investigation of immune response of patients who had pandemic virus A (H1N1) pdm09, radial hemolysis reaction demonstrated not only primary detection of antibodies to virus-agent (67%) during pandemic, but also elective heightened sensibility in the zone of low titer serums (1:20) in hemagglutination-inhibition reaction. These characteristics are very important in analysis of antibodies levels at early stages of disease. The radial hemolysis reaction continues to be a reliable instrument in evaluating qualitative and quantitative indicators of humoral immunity in ill patients and persons inoculated with new strains of human influenza virus.

An indirect enzyme immunoassay (EIA) using the purified fraction of surface viral glycoproteins (GP) as an antigen for solid phase sensitization was not shown to be a specific method for the differential detection of influenza A(HS) (HS-Ab) virus antibodies (Abs) due to total conservative epitopes in the structure of GPs of influenza A(H5) and A(H1NI) viruses. The cross activity of some monoclonal Abs (MAbs) to influenza A(H5) and A(HIN1) viruses, which had been obtained at the Research Institute of Influenza, was proof of the presence of total immunodominant determinants in the structure of influenza H1 and H5 virus hemagglutinin (HA). In this connection, an EIA, which was based on the competition of influenza A(H5) H5-Ab virus HA-specific MAbs in the test sera for an association with influenza A(H5) virus, was proposed for the subtype-specific detection of H5 Ab. Comparison of the results of competitive EIA (cEIA), microneutralization (MN) test and HA inhibition test (HAIT) (using equine red blood cells) in the examination of sera obtained from 44 volunteers immunized with inactivated vaccine containing influenza A/Indonesia/5/2005 (H5N1) virus showed the high sensitivity and specificity of cEIA in detecting H5-specific Abs. The effectiveness of cEIA for the sera strictly positive for the content of H5 Abs was close to that of MN test and was 9-34% higher than HAIT (depending on those used in the analysis of H5 virus antigens). cEIA may be proposed to assess new influenza vaccines as an additional laboratory test. Since the infectious virus is not used during cEIA, it may be recommended for the serodiagnosis of influenza A(H5) at practical virological laboratories.

Influenza virus recombinants between epidemic strains A/Brazil/11/78 (H1N1), A/USSR/382/78 (H3N2) and vaccine strains A/Leningrad/9/46 (H1N1), A/Victoria/35/72/50 (H3N2) have been tested for virulence for humans and albino mice; their genome structure has also been determined. It has been shown that after the replacement of surface antigens of A/Leningrad/9/46 (H1N1) strain by surface antigens of A/Brazil/11/78 (H1N1) or A/USSR/382/78 (H3N2), strains, the virus becomes totally nonpathogenic for mice whereas its virulence for humans is enhanced. The combination in recombinant X/28 (H1N1) of haemagglutinin and neuraminidase of A/Brazil/11/78 (H1N1) virus and othercomponents of A/Leningrad/9/46 virus determines its high affinity to the epithelium of the upper respiratory tract of humans, as well as its marked virulence for seronegative volunteers. Genetic mechanisms of influenza virus virulence and the involvement of surface proteins in its specific manifestations are discussed. It has been shown that pathogenic properties and the affinity of the virus to particular tissues are determined by different genes and their reasortment can result in the appearance of essentially new properties in recombinants.

The effect of vaccine dilution and composition on indices of vaccination activity was studied in a live allantoic influenza vaccine administered intranasally to adults. The vaccine was shown to be usable in a 1:1 (instead of 1:5) dilution without risk of its reactogenicity rising. An inhibition of component A(H3N2) was observed in a bivalent vaccine obtained by combining directly before use two monovalent vaccines, A(H1N1) and A(H3N2). The conclusions and recommendations based on the results of the present study have practical implications in influenza control.