Discussion
convalescents, Sputnik-Light vaccine
ADVERSE EVENTS, VIRUS
The ubiquitous spread of the SARS-CoV-2 virus requires not only specific prevention among adults but also the extension of vaccination coverage to young individuals under the age of 18 years.Compared to other vaccination modalities (e.g. single shot or two dose homologous), the heterologous prime-boost vaccination schedule seemed to be the more effective option for providing robust and long-term protection from COVID-19 (The safety analysis of the vaccine revealed both the 1/10 and 1/5 doses to be safe and well tolerated for the 12-to-17-year-old participants. The adverse events reported after vaccination of adolescents with 1/10 or 1/5 doses of Sputnik V were generally similar to those reported in adult volunteers vaccinated with the full dose of Sputnik V or the single dose of Sputnik-Light vaccine (equal to the first component of the Sputnik V vaccine) (The analysis of the humoral immune response dynamics demonstrated a dome-shaped antigen-specific IgG response, over 180 days of the study, regardless of the dose. After vaccination, a significant increase in IgG was detected, reaching its maximum by day 42 and then gradually decreasing. At the same time, the analysis of the dynamics of neutralizing antibodies over 180 days of the study found neutralizing antibodies to reach their peak values by day 90 of the study and remain at the same level on day 180. We assume that the different dynamics of the antibody response of antigen-specific IgG and neutralizing antibodies upon Sputnik V vaccination to be related to the affinity maturation of serum antibodies which was initially observed in COVID-19 convalescents (The emergence and spread of new SARS-CoV-2 virus variants led us to analyze further the level of neutralizing antibodies to the Delta variant (the most common variant of SARS-CoV-2 “serotype 1” and the Omicron variant sublineage BA.5 (the actual variant at the time of the manuscript writing) (This research has some limitations as it is the initial examination of the Gam-COVID-Vac (Sputnik V) vaccine in adolescents aged 12–17 years, with the primary aim of assessing safety and immunogenicity. Thus, the efficacy analysis was not the aim of the study. In addition, the sample size of the present study was insufficient to analyze rare and very rare adverse events which are to be investigated in the near future.The advantage of this study was the duration of the follow-up of the volunteers. A six-month period allowed us to assess not only the safety of the vaccine in volunteers aged 12–17 years but also the dynamics of the humoral immune response. The study of the immune response duration demonstrated that the neutralizing antibodies reached their maximum by day 90th day of the study, with the level remaining stable until day 180, justifying that the revaccination period should not be earlier than half of the year.In conclusion, the obtained data indicate the Gam-COVID-Vac vaccine at both doses (1/10 and 1/5 of the adult dose) in 12–17-year-old volunteers to be safe, well tolerated, and not to cause serious adverse events. Whereas immunogenicity differed in dose-dependent manner: administering a dose of 1/5 led to a more robust immune response in adolescents than a dose of 1/10. The results obtained prompted the selection of a higher (1/5 of the adult dose) vaccine dose of Sputnik V for immunisation of adolescents that has been given a separate name, Gam-Covid-Vac M (or Sputnik M vaccine). The chosen dose will be used in further multicenter, randomised, double-blind, placebo-controlled Phase 3 study in 3000 12-to-17-year-old adolescents (which is the stage II of the same The results of Phase 1/2 clinical trials have served as the basis for the provisional vaccine approval for clinical use issued on November 24, 2021 (registration number LP-007632)