The goal of this clinical study is to prove the no less immunogenicity of the Grippol Quadrivalent vaccine compared to the Grippol plus vaccine in children aged 6 months to 5 years (inclusive) for three identical strains of the compared vaccines in terms of the "proportion of vaccinated with seroconversion in paired sera of the hemagglutination inhibition reaction obtained before and after vaccination".

The main questions it aims to answer are:

1. To compare the immunogenicity of the Grippol Quadrivalent vaccine compared to the Grippol plus vaccine in children aged 6 months to 5 years (inclusive) for three identical strains of the compared vaccines in terms of "geometric mean antibody titers after vaccination"

2. Evaluate the immunogenicity of the Grippol Quadrivalent vaccine and the Grippol plus vaccine according to the following indicators:

   • Proportion of those vaccinated with seroconversion and geometric mean titer of antibodies to the fourth additional strain of compared vaccines
   • Multiplicity of the increase in the geometric mean titer of antibodies to 4 strains of the influenza virus in paired sera of the hemagglutination inhibition reaction after vaccination in relation to the initial values of antibody titers
   • Seroprotection (proportion (%) vaccinated with antibody titer ≥ 1:40 to 4 strains of influenza virus in paired sera of the hemagglutination inhibition reaction after vaccination)

3. Evaluate the effectiveness of the Grippol Quadrivalent vaccine and the Grippol plus vaccine according to the following indicators:

   • Incidence of Influenza and ARI (Month 1-Month 6 after vaccination)
   • Severity and duration of reported cases of influenza and ARI, presence of complications

4. Assess the reactogenicity of the Grippol Quadrivalent vaccine and the Grippol plus vaccine in children aged 6 months to 5 years (inclusive):

   • Frequency and nature of general and local post-vaccination reactions (7-day follow-up period after vaccine administration)

5. Assess the safety of Grippol Quadrivalent and Grippol Plus in children aged 6 months to 5 years (inclusive)

Inclusion Criteria:

1. Male and female children aged 6 months to 5 years inclusive at the time of vaccination.
2. Availability of Informed consent to participate in the study, signed by one of the parents.
3. The diagnosis is "healthy", established according to standard clinical, laboratory and instrumental methods of examination carried out at screening, according to the assessment of the researcher, as well as anamnesis data (absence of acute and chronic diseases of the respiratory, cardiovascular, nervous systems, dysfunction liver or kidneys).
4. Negative result of a rapid test for SARS-CoV-2 antigen at screening.
5. For children aged 6 to 11 months inclusive: children born at gestational age ≥37 weeks weighing ≥2.5 kg.
6. Parental consent to cooperate in good faith with the investigator and center staff, attend scheduled visits, complete the self-monitoring diary, and follow the protocol.

Exclusion Criteria:

1. Vaccination with any influenza vaccine within the previous 6 months. Vaccination with other vaccines, according to the national vaccination schedule, is allowed no later than 30 days before the introduction of the study vaccine, and no earlier than 30 days after the administration of the study vaccines.
2. Participation in a clinical trial of a vaccine, medicinal product, or medical device less than 30 days prior to screening.
3. Hypersensitivity to any of the components of the studied vaccines or severe post-vaccination complications to any vaccine in history.
4. The presence at the time of screening of acute infectious diseases of any localization, or the presence of a history of acute infectious and non-infectious diseases less than 14 days before screening.
5. Body temperature in the armpit ≥37.0°C at screening or before the introduction of the vaccine.
6. History of significant chronic diseases, such as malignant neoplasms or blood diseases, autoimmune diseases, insulin-dependent diabetes mellitus, chronic diseases of the lungs, liver or kidneys, cardiovascular, nervous systems, secondary, primary and induced immunodeficiency, HIV- infections, as well as other significant, according to the researcher, diseases.
7. A history of seizures or a progressive neurological disease.
8. History of Guillain-Barré syndrome (post-infectious demyelinating polyradiculoneuropathy of autoimmune etiology).
9. Use of antipyretics, including non-steroidal anti-inflammatory drugs less than 24 hours before screening and vaccination; antibacterial drugs of systemic action - less than 72 hours before screening and vaccination; anticoagulants - less than 3 weeks before screening and vaccination; immunoglobulins, blood products - less than 3 months before screening and vaccination; long-term use of systemic corticosteroids (prednisolone or equivalent for more than 2 consecutive weeks) - less than 3 months before vaccination screening.
10. Surgery performed less than 3 months prior to screening.
11. Children of research team members or research facility staff involved in this clinical trial.
12. Orphans, children left without parental care.
13. Any other medical or social condition that, in the opinion of the investigator, precludes the participation of the child in this study.