Antibody titers were presented as geometric mean titers (GMTs).

The GMFR is defined as the geometric mean of the within-subject ratios of the post-vaccination reciprocal HI titer to the pre-vaccination reciprocal HI titer for the vaccine virus.

Seroprotection rate is defined as the number of participants with HI titer value greater than or equal to (\>=) 1:40 which is considered as indicating protection.

Solicited administration site events included pain, redness and swelling.

Solicited administration site events included pain, redness and swelling.

Solicited systemic events included fatigue, fever, headache, muscle ache, joint pain, shivering (chills), sweating, gastrointestinal symptoms (nausea, vomiting, diarrhea, abdominal pain). Fever is defined as temperature \>=38 degrees Celsius (°C) for oral route (preferred location for measuring temperature).

Solicited systemic events included fatigue, fever, headache, muscle ache, joint pain, shivering (chills), sweating, gastrointestinal symptoms (nausea, vomiting, diarrhea, abdominal pain). Fever is defined as temperature \>=38 degrees Celsius (°C) for oral route (preferred location for measuring temperature).

Hemoglobin, white blood cells (WBC) increase, WBC decrease, platelets, neutrophils, lymphocytes and eosinophils were graded by FDA toxicity grading scale in which grades are Grade 1 = mild, Grade 2 = moderate, Grade 3 = severe and Grade 4 = potentially life threatening. Blood samples were collected for safety laboratory tests from the first 50% of participants of each age and dose group, at 7 days following each vaccination (i.e., Visit 2 and Visit 4).

Hemoglobin, WBC increase, WBC decrease, platelets, neutrophils, lymphocytes and eosinophils were graded by FDA toxicity grading scale in which grades are Grade 1 = mild, Grade 2 = moderate, Grade 3 = severe and Grade 4 = potentially life threatening. Blood samples were collected for safety laboratory tests from the first 50% of participants of each age and dose group, at 7 days following each vaccination (i.e., Visit 2 and Visit 4).

Sodium increase, sodium decrease, potassium increase, potassium decrease, creatinine, alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase, total bilirubin and blood urea nitrogen (BUN) were graded by FDA toxicity grading scale in which grades are Grade 1 = mild, Grade 2 = moderate, Grade 3 = severe and Grade 4 = potentially life threatening. Blood samples were collected for safety laboratory tests from the first 50% of participants of each age and dose group, at 7 days following each vaccination (i.e., Visit 2 and Visit 4).

Sodium increase, sodium decrease, potassium increase, potassium decrease, creatinine, ALT, AST, alkaline phosphatase, total bilirubin and BUN were graded by FDA toxicity grading scale in which grades are Grade 1 = mild, Grade 2 = moderate, Grade 3 = severe and Grade 4 = potentially life threatening. Blood samples were collected for safety laboratory tests from the first 50% of participants of each age and dose group, at 7 days following each vaccination (i.e., Visit 2 and Visit 4).

An unsolicited adverse event is defined as an adverse event that was either not included in the list of solicited events or could be included in the list of solicited events but with an onset outside the specified period of follow-up for solicited events.

An unsolicited adverse event is defined as an adverse event that was either not included in the list of solicited events or could be included in the list of solicited events but with an onset outside the specified period of follow-up for solicited events.

MAE is defined as an AE that results in an unscheduled visit to a medical professional (e.g., symptoms or illnesses requiring a hospitalization, emergency room visit, or visit to/by a healthcare provider).

An SAE is defined as any untoward medical occurrence that results in death, is life-threatening, requires hospitalization or prolongation of existing hospitalization, results in persistent or significant disability/incapacity, is a congenital anomaly/birth defect, is an abnormal pregnancy outcome (e.g., spontaneous abortion, fetal death, stillbirth, congenital anomalies, ectopic pregnancy), or is a suspected transmission of any infectious agent via an authorized medicinal product.

pIMDs are defined a subset of AEs of special interest that includes autoimmune diseases and other inflammatory and/or neurologic disorders of interest which may or may not have an autoimmune etiology.