Phase 1/2 Study of TAK-850 Intramuscular Injection in Healthy Pediatric Participants

Inclusion Criteria

• In the opinion of the investigator or the subinvestigator, the participant and/or his/her representative and his/her guardian is capable of understanding and complying with protocol requirements.
• The participant's representative can sign and date a written, informed consent form prior to the initiation of any study procedures.
• The participant is a healthy Japanese child.
• The participant is aged 6 months to 19 years, inclusive, at the time of starting to receive the study vaccine.
• A female participant of childbearing potential who is sexually active with a nonsterilized male partner agrees to routinely use adequate contraception from signing of informed consent until 12 weeks after the administration.

Exclusion Criteria

[Only for participants at the age of 6-35 months old]

• The participant is a preterm newborn (gestational age was less than 37 weeks) or a low-birth-weight newborn (birth weight was less than 2500 g).
• The participant has received any investigational compound within 4 months prior to the initial injection of study vaccine.
• The participant has been vaccinated with seasonal influenza vaccine within 6 months prior to the initial injection of study vaccine.
• The participant has a history of influenza infection within 6 months prior to the initial injection of study vaccine.
• The participant is a study site employee, an immediate family member of such an employee, or in a dependent relationship with a study site employee who is involved in the conduct of this study (e.g., spouse, parent, child, sibling), or may consent under duress.
• The participant has uncontrolled, clinically significant manifestations of neurological, cardiovascular, pulmonary, hepatic, renal, metabolic, gastrointestinal, endocrine or other disorders, which may impact the ability of the participant to participate or potentially confound the study results.
• The participant has an armpit temperature ≥ 37.5°C prior to the initial injection of study vaccine on Day 1.
• The participant has any medically diagnosed or suspected immune deficient condition.
• The participant has an immune compromising condition or disease, or is currently undergoing a form of treatment or was undergoing a form of treatment that can be expected to influence immune response within 30 days prior to the initial injection of study vaccine. Such treatments include, but are not limited to, systemic or high dose inhaled corticosteroids (> 800 μg/day of beclomethasone dipropionate or equivalent; the use of inhaled and nasal steroids that do not exceed this level will be permitted), radiation treatment or other immunosuppressive or cytotoxic drugs.
• The participant has received antipyretics within 4 hours prior to the initial injection of study vaccine.
• The participant has a history of Guillain-Barré Syndrome, demyelinating disorders (including acute disseminated encephalomyelitis [ADEM] and multiple sclerosis) or convulsions.
• The participant has a functional or surgical asplenia.
• The participant has a rash, other dermatologic conditions or tattoos which may interfere with the evaluation of injection site reaction as determined by the Investigator.
• The participant has a history of, or is infected with the Hepatitis B Virus (HBsAgs), Hepatitis C Virus (HCV) or Human Immunodeficiency Virus (HIV).
• The participant has a known hypersensitivity to any component of TAK-850.
• The participant has a history of severe allergic reactions or anaphylaxis.
• The participant has a history of drug abuse (defined as any illicit drug use) or a history of alcohol abuse within 1 year prior to the initial injection of study vaccine or is unwilling to agree to abstain from alcohol and drugs throughout the study.
• The participant has received any blood products (e.g. blood transfusion or immunoglobulin) within 90 days prior to the initial injection of study vaccine.
• The participant has received a live vaccine within