To evaluate the safety and immunogenicity of quadrivalent influenza virus split vaccine in healthy population aged 3-8 years following different immunization procedures.

To evaluate the safety and immunogenicity of quadrivalent influenza virus split vaccine in healthy population aged 3-8 years following different immunization procedures, and the participants randomized to receive two injections of 0.5 mL quadrivalent influenza vaccine at day 0 and 28.

Inclusion Criteria:

• Healthy children aged 3-8 years. Volunteers are required to show vaccination certificate if they have not received a previous flu vaccine.
• Volunteers' legal guardian or client informed consent, voluntarily participate in and sign informed consent. (Volunteers over the age of 8 also need informed consent and signature)
• Volunteers' legal guardian or client has the ability (non-illiterate) to understand the study procedures, to use a thermometer, scale, and fill in a diary card as required, and be able to complete the clinical study in compliance with the clinical trial protocol.

Exclusion Criteria:

• The axillary temperature greater than 37.0℃ on the day of enrollment;
• Have suffered from influenza within previous 3 months or suffering currently (confirmed by either clinical, serological or microbiological methods);
• Have received any influenza vaccine (registered or experimental) within 6 months or be going to receive other influenza vaccine during the study period;
• Allergic to any component of the vaccine, or have a history of allergic reactions to gentamicin sulfate;
• A history of severe allergy to any vaccine or drug, or with a history of nervous system damage;
• Congenital malformations or developmental disorders, genetic defects, severe malnutrition, etc;
• Acute illness, severe chronic illness or acute attack of chronic disease on the day of vaccination;
• A history of live attenuated vaccination within 14 days prior to vaccination and a history of other vaccinations within 7 days prior to vaccination;
• Received immunoenhancement or inhibitor therapy within 3 months (continued oral or intravenous administration for more than 14 days);
• Congenital or acquired immune deficiency, HIV infection, lymphoma, leukemia or other autoimmune diseases;
• Have a history of asthma, the condition has been unstable for past two years and require treatment, such as emergency treatment, hospitalization, intubation or oral or intravenous administration of corticosteroids and so on;
• Have received blood or blood-related products;
• A history of convulsion, epilepsy, encephalopathy, guillain-barre syndrome, a history of mental illness or have a mental illness family history;
• A history of abnormal coagulation function (such as coagulation factor deficiency, coagulation disease);
• Planning to relocate before the end of the study or to leave for an extended period during the scheduled study visit;
• Participating in or planning to participate in other clinical trials in the near future;
• Any conditions judged by investigators that were inappropriate for participation in this clinical trial.

Receiving the second dose of vaccine

• Have a severe allergic reaction after receiving the first dose of vaccine;
• Serious adverse events occurred that were causally related to the first dose of vaccine injection；
• After receiving the first dose of vaccine, the researchers will decide whether the volunteer should participate in the study continued or not if the newly discovered feature or newly condition occurred on volunteer that do not meet the inclusion criteria or meet the exclusion criteria;
• Other reasons for exclusion considered by the investigator.

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