Study of the Infectivity, Safety and Immunogenicity of Two Recombinant, Live-Attenuated, B/HPIV3 Vectored Vaccines Expressing the Fusion Glycoprotein of HMPV Delivered by Nasal Spray to HPIV3-Seropositive Children 24 to <60 Months of Age

Inclusion Criteria: * ≥24 months of age and \<60 months of age at the time of inoculation * HAI Screening for HPIV3-neutralizing antibody is obtained within the calendar year of inoculation * Seropositive for HPIV3 antibody, defined as serum HPIV3 HAI titer \>1:8 * Pre-inoculation serum sample for HPIV3-neutralizing antibody specimen is obtained no more than 42 days prior to inoculation * In good health based on review of the medical record, history, and physical examination at the time of inoculation * Received routine immunizations appropriate for age based on the Advisory Committee on Immunization Practices (ACIP) Recommended Immunization Schedule for Children and Adolescents Aged 18 Years or Younger * Growing normally for age as demonstrated on a World Health Organization (WHO) growth chart, AND has a current height and weight above the 3rd percentile for age * Expected to be available for the duration of the study * Parent/guardian is willing and able to provide written informed consent Exclusion Criteria: * \<24 months of age and \>60 months of age at the time of inoculation. * Born at less than 34 weeks gestation * Maternal history of a positive HIV test before or during pregnancy. * Evidence of chronic disease * Known or suspected infection or impairment of immunological functions * Bone marrow/solid organ transplant recipient * Major congenital malformations, including congenital cleft palate or cytogenetic abnormalities * Suspected or documented developmental dis…