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

This randomized, double-blind, multi-center study will enroll approximately 200 children 24
to less than (<) 48 months of age. Participants will be randomized in a 1:1:1 ratio to
receive two doses of either FluMist quadrivalent 2017-2018, FluMist quadrivalent 2015-2016
formulation, or FluMist trivalent 2015-2016 formulation.

Participants will be screened within 30 days prior to randomization. Randomization will be
stratified according to whether the participant ever received prior influenza vaccination.
Approximately 50% of the participants will not have been previously vaccinated. All
participants will receive two doses of investigational product on Study Days 1 and 28, and
followed for a 28-day follow-up period after each dose. Blood and nasal samples will be
collected and safety evaluations perfomed.

The duration of participants participation is approximately 2 to 3 months. The study will be
conducted during the influenza "off-season" in the US. After completion of the study all
participants will be offered and strongly encouraged to receive an inactivated influenza
vaccine approved for use in the US for the 2017-2018 influenza season.

Key Inclusion Criteria:

- Age 24 months to < 48 months of age

- Healthy by medical history and physical examination or presence of stable underlying
chronic medical condition for which hospitalization has not been required in the
previous year

Key Exclusion Criteria:

- History of allergic disease or reactions likely to be exacerbated by any component of
the investigational product

- Acute illness or evidence of significant active infection (including fever >= 100.4
degrees Fahrenheit (38.0 degrees Celsius) at randomization

- History of asthma or history of recurrent wheezing

- Any known immunosuppressive condition or immune deficiency disease

- Current or expected receipt of immunosuppressive medications within a 28 day window
around vaccination

- Use of aspirin or salicylate-containing medications within 28 days prior to
randomization or expected receipt thru 28 days after vaccination

- Use of antiviral agents with activity against influenza viruses within 48 hours prior
to first dose of investigational product or anticipated use of such agents through the
end of the study follow-up period

- Receipt of any non-study seasonal influenza vaccine within 90 days of Dose 1 or
planned receipt of non-study seasonal influenza vaccine prior to 28 days after last
vaccination

- Receipt of immunoglobulin or blood products within 90 days before randomization into
the study or expected receipt during study participation

- Known or suspected mitochondrial encephalomyopathy

- History of Guillian-Barre syndrome

- Administration of intranasal medications within 10 days prior to randomization, for
expected receipt through 10 days after administration of each dose of investigational
product