Objectives: This study aimed to determine the safety, tolerability and immunogenicity of TetraFluBet, an inactivated subunit influenza vaccine that contains a corpuscular immuno-adjuvant derived from natural betulin. Methods: We conducted a prospective, randomized, open-labeled, single-center, phase I trial. The study was conducted in two stages: 5 volunteers in stage I and 25 volunteers in stage II. Eligible participants received one single dose (20 μg/0.5 mL) of TetraFluBet intramuscularly. Participants were followed for adverse events and reactogenicity. Seroconversion rate, seroprotection level, geometric mean titers (GMTs) of virus-neutralizing antibodies, IFN-γ induction and cell-mediated immunity were assessed. Results: A total of 30 participants were enrolled. No vaccine-related serious adverse events were observed. The proportions of study participants with 4-fold seroconversions assessed by the HI assay (with 95% CIs) were 80.0% (62.7; 90.5), 70.0% (52.1; 83.3), 63.3% (45.5; 78.1) and 73.3% (55.6; 85.8) for influenza virus subtypes A (H1N1), A (H3N2), B1 and B2, respectively. Seroprotection levels (with 95% CIs) were 83.3% (66.4; 92.7), 83.3% (66.4; 92.7), 73.3% (55.6; 85.8) and 66.7% (48.8; 80.8), respectively. The fold increases in the GMTs of virus-neutralizing antibodies for subtype H1N1 was 6.50, for subtype H3N2 was 3.03, for subtype B1 was 3.56 and for subtype B2 was 6.07. The population of cytotoxic T-cells increased significantly in the post-vaccination period, indicating a strong CD3⁺CD8⁺ response. Conclusions: TetraFluBet tetravalent inactivated subunit vaccine with adjuvant demonstrated pronounced immunogenic properties, leading to the formation of both specific humoral and cellular immunity at a 20 μg dose.

Influenza is well-known to have a considerable influence on healthcare system, therefore, vaccination plays a significant role in dealing with severe consequences. Close attention is paid to the development of tetravalent adjuvanted vaccines, containing antigens of two influenza A subtypes (H1N1, H3N2) and two influenza B subtypes (Victoria, Yamagata) to increase the effectiveness of influenza prevention. In this work we present the results of pre-clinical study of innovative subunit tetravalent candidate influenza vaccine, with addition of betulin as adjuvant, TetraFluBet. The study was conducted using female BALB/c mice, male and female mongrel rats and guinea pigs. TetraFluBet and commercially available vaccines were injected intraperitoneally twice in a 14-day interval after intranasal infection with 5LD50 and 10LD50. Chronic toxicity was assessed by immunohistochemistry of extracted organs and by hematological and biochemical blood parameters. Protectivity and immunogenicity were evaluated using hemagglutination inhibition and microneutralization with MDCK assays. Chronic toxicity study did not reveal any side effects of candidate TetraFluBet vaccine on both rats and guinea pigs. One vaccination dose of TetraFluBet provided 100% protectivity against all 4 influenza subtypes and significantly increased neutralizing antibody activity in response to immunization of influenza subtypes. Pre-clinical candidate vaccine TetraFluBet confirmed its safety along with specific activity, showed high immunogenicity and can be recommended for further clinical studies.