Evaluate the Shedding and Immunogencity of Different Formulations of FluMist in Children 24 to <48 Months of Age

Percentage of Participants Who Shed Vaccine Virus by Formulation, Strain, Dose Number, and Baseline Serostatus as Measured by Quantitative Reverse Transcriptase Polymerase Chain Reaction (qRT-PCR)

Quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) was used to measure viral shedding from the nasopharyngeal swabs. Percentage of participants who shed virus are reported.

Time frame: Days 2, 3, 4, 5, and 7 after Dose 1 (Day 1 dose) and on Days 2, 4, and 6 after Dose 2 (Day 28 dose)

Number of Days of Vaccine Virus Shedding by Formulation, Strain, Dose Number, and Baseline Serostatus as Measured by qRT-PCR

Quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) was used to measure viral shedding from the nasopharyngeal swabs. Number of days of virus shedding are reported.

Time frame: Days 2, 3, 4, 5, and 7 after Dose 1 (Day 1 dose) and on Days 2, 4 and 6 after Dose 2 (Day 28 dose)

Viral Titer by Day, Strain, Dose Number, and Baseline Serostatus as Measured by qRT-PCR

Quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) was used to measure viral titer from the nasopharyngeal swabs. Viral titers are reported.

Time frame: Day (D) 2, D3, D4, D5, and D7 after Dose 1 (D1 dose) and on D2, D4 and D6 after Dose 2 (D28 dose)

Percentage of Participants With Strain-specific Neutralizing Antibody Seroconversion Rates From Baseline Through Days 28 and 56 by Baseline Serostatus

Seroconversion rate is defined as \>= 4-fold rise from baseline in strain specific microneutralizing antibody titer. Baseline microneutralization values of less than or equal to (\<=) 10 were considered as microneutralization status negative and values greater than (\>) 10 were considered microneutralization positive. Percentage of participants with \>= 4-fold rise in strain specific neutralizing antibody titer at Days 28 and 56 are reported.

Time frame: Days 28 and 56

Percentage of Participants With Strain-specific Nasal Immunoglobulin A (IgA) Seroconversion Rate From Baseline Through Days 28 and 56

Seroconversion rate is defined as \>= 2-fold rise from baseline in strain speciific nasal IgA antibody titer. Percentage of participants with \>= 2-fold rise in strain speciific nasal IgA antibody titer at Days 28 and 56 are reported for this outcome.

Time frame: Days 28 and 56

Percentage of Participants With Any Post Dose Strain-specific Antibody Response

Strain specific antibody response defined as \>= 4-fold increase in HAI antibodies or \>= 4-fold increase in neutralizing antibodies or \>= 2-fold increase in IgA antibodies.

Time frame: Days 28 and 56

Percentage of Participants With Any Solicited Symptoms

Solicited symptoms included fever by any route (temperature \>= 100.4 degrees Fahrenheit), runny/stuffy nose, sore throat, cough, headache, generalized muscle aches, lethargy or tiredness/weakness, and decreased appetite.

Time frame: Day 1 through Day 14 after Dose 1 (Day 1 dose) and Dose 2 (Day 28 dose)

Number of Participants With Treatment-emergent Adverse Events (TEAEs) and Treatment-emergent Serious Adverse Events (TESAEs)

An Adverse Event (AE) is any unfavourable and unintended sign, symptoms, or diseases temporally associated with use of study drug, whether or not considered related to study drug. A serious adverse event (SAE) is an AE that results in death, initial or prolonged inpatient hospitalization, life-threatening, persistent or significant disability/incapacity, congenital anomaly/birth defect, or an important medical event. TEAEs and TESAEs are defined as AEs and SAEs present at baseline that worsened in intensity after administration of study drug, or events absent at baseline that emerged after administration of study drug.

Time frame: Day 1 through Day 28 after Dose 1 (Day 1 dose) and Dose 2 (Day 28 dose)