Understanding RSV

What is RSV?

RSV is a very contagious virus and the most common cause of bronchiolitis (inflammation of the small airways in the lung) and pneumonia in children younger than age 1 in the U.S.  Almost all children are infected with the virus by their second birthday, but only a small percentage of children develop severe illness.

What Causes RSV and How is it Spread?

  • RSV passes from person to person like a cold virus—when someone with RSV coughs or sneezes, droplets travel through the air to others nearby or land on surfaces that others will touch.
  • It can enter your body when you touch your eyes or nose after touching RSV germs.
  • RSV infection outbreaks happen mainly the winter. In warm climates, RSV infections generally occur during fall, winter, and early spring.
  • When an outbreak hits and how severe it may be varies from year to year.
  • RSV spreads rapidly among children during outbreaks; most children will have been infected with RSV sometime before 2 years 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, infants and children can continue to spread the virus for 1 to 3 weeks.

Who Gets RSV?

  • Anyone can get RSV. In adults, it seems like nothing more than a cold.
  • Most children get RSV by the time they turn two.
  • In infants and very young children, RSV can be severe.

People at risk for severe RSV are:

  • Infants and children born prematurely, who often have underdeveloped lungs and may not have received enough antibodies from their mothers to help them fight off RSV disease once they have been exposed to it. 
  • Boys under 6 months of age
  • Infants and children with chronic lung disease like cystic fibrosis
  • Infants and children with congenital heart disease
  • Infants in crowded day care settings
  • Anyone whose immune systems are weak due to illness or treatments
  • Elderly and adults with chronic heart or lung disease

How Does RSV Affect the Body?

  • RSV can cause upper respiratory infections (such as colds) and lower respiratory tract infections (such as bronchiolitis and pneumonia).
  • You can be infected with RSV several times during your lifetime. After each RSV infection, your body becomes more immune to the virus, but you are never completely immune.

How Serious is RSV?

  • RSV is most serious for infants younger than one year.
  • RSV is the leading cause of pneumonia and bronchiolitis (inflammation of the airways) in children under age one.
  • Children with RSV may need to be hospitalized. Most children hospitalized for RSV infection are under 6 months of age.
  • RSV is particularly dangerous for infants and children who were born prematurely. Premature children who are infected with RSV disease often need to be hospitalized.
  • RSV can cause the death of high-risk children.


People of any age can get another RSV infection, but later illnesses 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 they are reinfected.

Learn more about RSV symptoms, diagnosis and treatment