The purpose of this study is to define safety, immune response (ability of the body to fight infection), and virus shedding of a live PIV3 and RSV nasal vaccine, in comparison to another form of vaccination by a Placebo (an inactive sugar and salt solution). Both MEDI-534 and Placebo are administered as nose drops.

Study participation will last for about one year and will include a screening visit; 12 scheduled study visits and several telephone contacts. All children participating should be healthy and are scheduled to have a total of two blood tests. About 10ml (about 2 teaspoons) of blood will be collected over the course of the entire study. One blood test will be done prior to the first vaccination and another one done after 28 days after the last vaccination. There will also be 9 scheduled nasal rinses during the study where up to 11 teaspoons (about &14; cup) of nasal fluid will be taken for testing.

The criteria for selection of the children that can take part in the study are the following:

• Only one child per family can be in this study
• The children should be between the ages of 6 months and 2 years
• Children should not stay at home with a person working as a health care practitioner for patients with weakened immune systems, or a person working as a day care provider for infants younger than 6 months.

“The study is very important as there is currently no treatment for this condition. As many children as possible are required to complete this study and we appeal to the parents to assist us in that regard”, said Professor Robin Green - Head of Paediatrics and Child Health Department, University of Pretoria.