Respiratory syncytial virus (RSV) is a common respiratory virus that usually causes mild, cold-like symptoms. Most people recover in a week or two, but RSV can be serious, especially for infants and older adults. It is a significant cause of respiratory illness in young children.

The virus infects the lungs and breathing passages and can lead to severe conditions like bronchiolitis (inflammation of the small airways in the lung) and pneumonia (infection of the lungs). In severe cases, RSV infection can result in hospitalization, particularly in infants, children with underlying health conditions, and elderly individuals.