HMPV is a viral respiratory pathogen that was discovered in 2001, but studies have shown that it has been circulating in humans for at least 50 years. Older adults and adults with asthma who are infected with HMPV may be at increased risk for lower respiratory illness and hospitalization. In infants and young children, HMPV infection may cause upper or lower respiratory illness, ear infections, bronchiolitis, croup, pneumonia, and exacerbations of asthma. Children less than 2 years of age are most susceptible to severe HMPV infections, and HMPV is the second or third leading cause of viral lower respiratory illness in children. The National Institute of Allergy and Infectious Diseases (NIAID) is working to develop a live-attenuated, intranasally administered HMPV vaccine for use in infants. The purpose of this study is to evaluate the safety and immunogenicity of an HMPV vaccine.~The vaccine will be evaluated in four groups of participants: healthy adults; HMPV-seropositive children; and two groups of HMPV-seronegative infants and children, with each seronegative group receiving a different dose of the vaccine. In the adult group, participants will all receive the vaccine; in the infant and children groups, participants will be randomly assigned to receive either the vaccine or a placebo. Study researchers will review participants' study data and confirm the safety of the vaccine before enrolling the next group of participants.~This study will first enroll healthy adults. At a baseline study visit, all participants will undergo a medical history review, physical examination, nasal wash procedure, vital sign measurements, and a blood collection. They will then receive the vaccine, and they will remain in the clinic for 30 minutes for observation. Participants will record their temperature daily for 12 days. Additional study visits will occur at Days 3, 4, 5, 6, 7, 10, and 12. At each study visit, participants will undergo a medical history review, vital sign measurements, and a nasal wash procedure. A final study visit will occur on Day 28 and will also include a blood collection. The second group of participants will include seropositive children. They will receive the vaccine or a placebo vaccine and take part in the same study procedures as the adult participants. Participants' parents will receive telephone calls or e-mails from study staff on Days 1, 2, 8, 9, 11, and 13 to obtain and record medical history and temperature readings. The third and fourth groups of participants will include seronegative infants and children. Each of these two groups will receive different doses of the vaccine or placebo vaccine. They will attend study visits on Days 3, 5, 7, 10, 12, 14, 17, 19, 21, 28, and 56, and they will undergo the same study procedures as the other participants. Parents of seronegative infants and children will receive telephone calls or e-mails from study staff on Days 1, 2, 4, 6, 8, 9, 11, 13, 15, 16, 18, 20, 22 to 27, and 29.~Study staff will call all participants at Month 6 for a medical history review and follow up.
People who are infected with human metapneumovirus (HMPV) may develop upper and lower respiratory illnesses. Children are particularly sensitive to HMPV infection. This study will evaluate the safety and immune response of an HMPV vaccine in healthy adults, HMPV-seropositive children, and HMPV-seronegative infants and children.