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Infection and Incidence

Baby girl

RSV can cause upper respiratory infections (such as colds) and lower respiratory tract infections (such as bronchiolitis and pneumonia). In children younger than 1 year of age, RSV is the most common cause of bronchiolitis, an inflammation of the small airways in the lung, and pneumonia, an infection of the lungs.

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 out of 100 of them have signs or symptoms of bronchiolitis or pneumonia, and 
  • 5 to 20 out of 1,000 will require hospitalization. Most children hospitalized for RSV infection are younger than 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 infections later in life are generally less severe. Premature infants, children younger than 2 years of age with congenital heart or chronic lung disease, and children with compromised (weakened) immune systems due to a medical condition or medical treatment are at highest risk for severe disease. Adults with compromised immune systems and those 65 and older are also at increased risk of severe disease.

In the United States and other areas with similar climates, RSV infections generally occur during fall, winter, and spring. The timing and severity of RSV circulation in a given community can vary from year to year.

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