Infection and Incidence

RSV can cause upper respiratory infections (such as colds) and lower respiratory tract infections (such as bronchiolitis and pneumonia). In children under 1 year of age, RSV is the most important cause of bronchiolitis, an inflammation of the small airwaysin the lung.

Almost all children will have had an RSV infection by their second birthday. When infants and children are exposed to RSV for the first time, 25% to 40% of them have signs or symptoms of bronchiolitis or pneumonia, and 0.5% to 2% will require hospitalization. Most children hospitalized for RSV infection are under 6 months of age.

Infants and children infected with RSV usually show symptoms within 4 to 6 days of infection. Most will recover in 1 to 2 weeks. However, even after recovery, very young infants and children with weakened immune systems can continue to spread the virus for 1 to 3 weeks.

People of any age can get another RSV infection, but later infections are generally less severe. The elderly and adults with chronic heart or lung disease or with immune systems weakened by medical conditions or treatments remain at high risk for developing severe RSV disease if reinfected.

In temperate climates, RSV infections generally occur during fall, winter, and early spring. The timing and severity of RSV circulation in a given community can vary from year to year.