Evaluating the Safety and Immunogenicity of a Human Parainfluenza Type 3 (HPIV3) Virus Vaccine in Infants and Children

Human parainfluenza viruses can cause serious respiratory tract disease in infants and children under 5 years of age, and approximately 25% of children under 5 years of age have experienced a clinically significant parainfluenza virus infection. HPIV3, one of the four types of the parainfluenza virus, can cause pneumonia, bronchiolitis, croup, and bronchitis, and virtually all children have experienced primary HPIV3 infections by the time they are 3 to 4 years of age. In the United States, HPIV3 is responsible for approximately 11% of hospitalizations for respiratory diseases in children. Because HPIV3-associated lower respiratory illness typically occurs in the first year of life, the need exists for an HPIV3 vaccine that is safe and effective in infants. The purpose of this study is to evaluate the safety and immunogenicity of two doses of a live attenuated HPIV3 vaccine in infants and young children. This study will enroll healthy, HPIV3 seronegative infants and children 6 months to 36 months of age. Participants will be randomly assigned to receive either the HPIV3 vaccine or a placebo vaccine. At a baseline study visit, all participants will undergo a medical history review, physical examination, vital sign measurements, and a nasal wash procedure. They will then receive their assigned vaccine in the form of nose drops. Participants will remain in the study clinic for 30 minutes after the vaccination for monitoring. Participants' parents will receive a thermometer and will record participants' temperature for 18 days after the vaccination. Study staff will call participants' parents on Days 1-18, 84, 112, and 140 to monitor participants' temperature and medical status. Study visits will occur 3, 6, 12, and 56 days after the vaccination, and participants will undergo similar tests and procedures as at the vaccination visit; a blood collection will also occur at Day 56. Six months after the first vaccination, all participants will return to the clinic and receive the second vaccination. All study procedures and study visits that followed the first vaccination will be repeated, and participants' last follow-up visit will occur 31 days after the second vaccination.