A Phase 1/2A Study to Evaluate the Safety, Immunogenicity, and Shedding of MEDI-560 in Infants 1 to < 12 Months of Age

Inclusion Criteria:

1. Male or female whose age on the day of randomization falls within one of the two age cohorts:

   Cohort 1: 6 to < 12 months (≥ 6 months of age and not yet reached their 1st year birthday); Cohort 2: 1 to < 3 months (> 28 days of age and not yet reached their 3rd month birthday)

2. Cohort 1 only: Participant is seronegative to HPIV3 at screening as determined by ELISA; or the legal representative is willing to provide access to data documenting that the participant was screened for another MedImmune trial after written informed consent was obtained, and that the participant is seronegative to HPIV3 within 21 days prior to randomization into MI-CP150 as determined by ELISA at MedImmune
3. Participant was the product of a normal full term pregnancy, defined as 36-42 weeks gestation
4. Participant is in general good health
5. Participant's legal representative is available by telephone
6. Written informed consent and Health Insurance Portability and Accountability Act authorization (if applicable) obtained from the participant's legal representative
7. Participant's legal representative is able to understand and comply with the requirements of the protocol as judged by the investigator
8. Participant is available to complete the follow-up period of 180 days after the final dose of investigational product as required by the protocol
9. Participant's legal representative is willing and able to bring the subject to the study site for evaluation of respiratory illness in accordance with the protocol

Exclusion Criteria:

1. Any fever (≥ 100.4°F [≥ 38.0°C], regardless of route) or lower respiratory illness within 7 days prior to randomization
2. Moderate or severe nasal congestion that in the investigator's opinion could prevent intranasal delivery of investigational product
3. Cohort 1 only: weight < the fifth percentile for age on the day of randomization
4. Cohort 2 only: history of low birth-weight (ie, < 2,500 grams at birth) or weight < fifth percentile for age on the day of randomization
5. 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 investigational product dosing, except that infrequent use of over-the-counter medications such as pain relievers are permitted according to the judgment of the investigator
6. Any current or expected receipt of immunosuppressive agents including steroids (≥ 2 mg/kg per day of prednisone or its equivalent, or ≥ 20 mg/day if the participant weighs >10 kg, given daily or on alternate days for ≥ 14 days); children in this category should not receive investigational product until immunosuppressive agents including corticosteroid therapy have been discontinued for ≥ 30 days; the use of topical steroids is permitted according to the judgment of the investigator
7. History of receipt of blood transfusion or expected receipt through 30 days after final investigational product dosing
8. History of receipt of immunoglobulin products or expected receipt through 30 days after final investigational product dosing
9. Receipt of any investigational drug within 60 days prior to randomization or expected receipt through 30 days after final investigational product dosing
10. 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 dose
11. Receipt of any inactivated (eg, non-live) vaccine or rotavirus vaccine within 14 days prior to randomization or expected receipt within a 14-day window around any dose
12. Known or suspected immunodeficiency, including human immunodeficiency virus
13. Living in the same home or enrolled in the same classroom at day care with infants < 24 months of age within 28 days after each dose (only one child per household may be enrolled into the study)
14. Contact with pregnant caregiver within 28 days after each dose
15. Household contact with an immunocompromised person within 28 days after each dose; the participant should also avoid close contact with immunocompromised individuals for at least 28 days after each investigational product dose
16. Household contact within 28 days after each dose with a healthcare worker who has direct patient care responsibilities or household contact within 28 days after each dose with someone who is a day care provider or preschool teacher for children < 24 months of age
17. History of allergic reaction to any component of the investigational product
18. Previous medical history or evidence of an intercurrent or chronic illness that, in the opinion of the investigator, may compromise the safety of the participant
19. Known or suspected active or chronic hepatitis infection
20. History of medical diagnosis of asthma, reactive airway disease, wheezing requiring medication, bronchoconstriction or treatment with a β2 agonist (eg, albuterol), cystic fibrosis, chronic lung disease of prematurity (eg, bronchopulmonary dysplasia), chronic pulmonary disease, medically confirmed apnea, hospitalization for respiratory illness or mechanical ventilation
21. A family member or a household contact who is an employee of the research center or otherwise involved with the conduct of the study
22. Any condition that, in the opinion of the investigator, might interfere with investigational product evaluation