Safety and Tolerability Study to Evaluate MEDI-534 in Children 6 to < 24 Months of Age

The overall objective of the MEDI-534 clinical development program is to evaluate the safety, efficacy and tolerability of MEDI-534 for the prevention of serious RSV and PIV3 disease in young infants.

The primary objective of this study is to describe the safety and tolerability of multiple doses of MEDI-534 at 10\^4, 10\^5, or 10\^6 TCID50 when administered to RSV and PIV3 seronegative children 6 to \<24 months of age.

Eligibility Criteria:
Inclusion Criteria:

* Male or female whose age on the day of randomization is 6 to \<24 months (reached 6th month birthday and not yet reached 2nd year birthday)
* Subject is seronegative to both RSV and PIV3 at screening
* Subject was the product of normal full term pregnancy (defined as \>36 weeks gestation)
* Subject is in general good health
* Subject's legal representative is available by telephone
* Written informed consent and HIPAA authorization (if applicable) obtained from the subject's legal representative
* Subject's legal representative is able to understand and comply with the requirements of the protocol as judged by the investigator
* Subject is available to complete the follow-up period, which will be through the end of RSV season (provisionally defined as 01/Apr for the United States) or 180 days after the final dose of study vaccine, whichever is later
* Subject's legal representative must be willing and able to bring the subject to the study site for evaluation of respiratory illness in accordance with the protocol

Exclusion Criteria:

* Any fever (equal to or greater than 100.4°F \[equal to or greater than 38.0°C\], regardless of route) or lower respiratory illness (Section 4.1.2) within 7 days prior to randomization
* Moderate or severe nasal congestion that in the investigator's opinion could prevent intranasal delivery of vaccine
* Any drug therapy (chronic or other) within 7 days prior to randomization or expected receipt through the protocol-specified blood collection 28 days after each study vaccine dosing, except that infrequent use of over-the-counter medications such as pain relievers are permitted according to the judgment of the investigator
* Any current or expected receipt of immunosuppressive agents including steroids (2 mg/kg per day of prednisone or its equivalent, or equal to or greater than 20 mg/day if the subject weighs \>10 kg, given daily or on alternate days for equal to or greater than 14 days); children in this category should not receive study vaccine until immunosuppressive agents including corticosteroid therapy have been discontinued for equal to or greater than 30 days; the use of topical steroids is permitted according to the judgment of the investigator
* History of receipt of blood transfusion or expected receipt through 30 days following final study vaccine dosing
* History of receipt of immunoglobulin products or expected receipt through 30 days after study vaccine dosing
* Receipt of any investigational drug within 60 days prior to randomization or expected receipt through 30 days after final study vaccine dosing
* Receipt of any live virus vaccine (excluding rotavirus vaccine) within 28 days prior to randomization or expected receipt within a 28-day window around any study vaccine dose
* Receipt of any inactivated (i.e., non-live) vaccine or rotavirus vaccine within 14 days prior to randomization or expected receipt within a 14-day window around any study vaccine dose
* Known or suspected immunodeficiency, including HIV
* Living in the same home or enrolled in the same classroom at day care with infants \<24 months of age (only one child per household may be enrolled into the study)
* Contact with pregnant caregiver
* A household contact who is immunocompromised; the subject should also avoid close contact with immunocompromised individuals for at least 30 days after any study vaccine dose
* A household contact who is a health care provider in contact with immunocompromised patients or who is a day care provider for infants under the age of 6 months
* History of allergic reaction to any component of the study vaccine
* Previous medical history, or evidence, of an intercurrent or chronic illness that, in the opinion of the investigator, may compromise the safety of the subject
* Known or suspected active or chronic hepatitis infection
* History of medical diagnosis of asthma, reactive airway disease, wheezing requiring medication, cystic fibrosis, bronchopulmonary dysplasia, chronic pulmonary disease, medically confirmed apnea, hospitalization for respiratory illness or mechanical ventilation
* Family member or household contact who is an employee of the research center or otherwise involved with the conduct of the study
* Any condition that, in the opinion of the investigator, might interfere with study vaccine evaluation