A Phase I Study of the Safety and Immunogenicity of the Recombinant Live-Attenuated Human Parainfluenza Type 2 Virus Vaccine, rHPIV2 15C/948L/Δ1724 Lot PIV2#109C, Delivered as Nose Drops to Adults 18 to 49 Years of Age, HPIV2-Seropositive Children 15 to 59 Months of Age, and HPIV2-Seronegative Infants and Children 6 to 59 Months of Age

HPIV2 is a virus that can cause severe respiratory illnesses, such as pneumonia and bronchiolitis, in infants and young children. Approximately 3% of all hospitalizations for respiratory tract diseases among infants and children are the result of HPIV2. Efforts to develop a vaccine for HPIV2 have focused on a live attenuated intranasally administered vaccine, a type of vaccine that uses a live virus that has been modified to make it weaker and easier for the immune system to get rid of. This approach is useful for several reasons: it activates two of the body's natural defenses, the antibody-mediated and the cell-mediated responses; it is immunogenic in infants who still have maternal antibodies; and it induces a mucosal immune response. This study will test the safety and immunogenicity of an HPIV2 vaccine in adults, children, and then infants.

This study will have four groups and will proceed in a step-wise fashion. The first group will consist only of adults receiving the HPIV2 vaccine. If it is deemed safe after that, children from ages 15 to 59 months who already have HPIV2 antibodies will be randomly assigned to receive either the vaccine or a placebo. The third group includes infants and children from 6 to 59 months old who do not have HPIV2 antibodies and will be randomly assigned either a lower dose of the vaccine or a placebo. The fourth group also includes infants and children from 6 to 59 months old who do not have HPIV2 antibodies and will be randomly assigned a standard dose vaccine or placebo. The vaccine will be administered as a nose drop in a single dose for all groups.

Assessments for the first two groups will take place over the 11 days following administration of the vaccine and at a 28-day follow-up. The third and fourth groups will include 22 days of assessments after vaccination, one assessment between Days 23 and 26, and assessments on Days 27, 28, 29, and 56. Measures will include a clinical assessment, a nasal wash, a phone report, and taking a temperature. Measurement of serum HPIV2 antibodies will take place at baseline and after 28 (for groups one and two) or 56 (for groups three and four) days.