• To compare immune responses to measles, mumps, rubella, and varicella antigens following vaccination in children who receive FluMist concurrently with MMRIIÒ and VARIVAXÒ and in children who receive an intranasal placebo mist concurrently with MMRIIÒ and VARIVAXÒ (Group 2 vs. Group 1).
• To compare immune responses to the three strains of influenza (H1N1, H3N2, and B) following a two dose regimen of FluMist in children who receive the initial FluMist dose concurrently with MMRIIÒ and VARIVAXÒ and in children who receive two doses of FluMist alone (Group 2 vs. Group 3).Secondary:
• To assess the safety and tolerability of concurrent administration of FluMist with MMRIIÒ and VARIVAXÒ.

Inclusion Criteria:

• 12 to 15 months of age (not reached their 16th month birthday);
• In good health;
• Parent/guardian available by telephone or for home visits;
• Ability of the parent/guardian to understand and comply with the requirements of the protocol;
• Signed informed consent by parent/guardian; and
• Up to date with the primary series of recommended vaccines per standard clinic practice and local vaccine availability.

Exclusion Criteria:

• Previous known measles, mumps, rubella or varicella disease;
• Previous vaccination against measles, mumps, rubella or varicella disease;
• Hypersensitivity to egg or egg protein;
• Signs or symptoms of any immunosuppressive or immune deficiency disease or ongoing immunosuppressive therapy; or an immunosuppressed individual living in the same household;
• Acute febrile (>100.0oF [37.8°C] oral) illness or clinically significant upper respiratory illness within the 72 hours prior to enrollment;
• Use of aspirin (acetylsalicylic acid) or aspirin-containing products in the month prior to enrollment, or expected use of aspirin while enrolled in this study;
• Administration of any intranasal medication within two weeks prior to enrollment or expected receipt during this study;
• Administration of any live virus vaccine within one month prior to enrollment through 30 days after Visit 3;
• Administration of any inactivated vaccine within two weeks prior to enrollment through 30 days after Visit 3;
• Participation in another investigational trial within one month prior to enrollment or expected enrollment in another investigational trial during this study;
• Receipt of any blood product within three months prior to vaccination or expected receipt within the study duration; and
• Any condition which, in the opinion of the investigator, would interfere with the interpretation or evaluation of the vaccines.
• History of two or more episodes of medically attended wheezing illness by parent/guardian report.
• History of medically attended wheezing illness or bronchodilator medication use within four weeks of enrollment by parent/guardian report.