Babies younger than 1 year of age and other young children who become infected with respiratory syncytial virus (RSV) have a high risk of developing complications, such as bronchiolitis or pneumonia.

Babies who have a high risk of developing complications from RSV include those who:

• Are less than 6 months old.
• Were born early (premature).
• Have existing heart or lung disease.

Babies or children who have certain conditions are at a higher risk of developing complications from RSV. These conditions include:

• Congenital heart disease.
• Chronic lung disease, also known as bronchopulmonary dysplasia, and cystic fibrosis.
• An impaired immune system, which can involve various health factors. For example, having a severe chronic illness, such as cancer, can affect the immune system. In addition, certain medicines, such as chemotherapy or steroids, suppress the immune system.
• Exposure to tobacco smoke.