RSV, the “respiratory syncytial virus”, is the virus at the origin of a very common respiratory infection in infants; however, it can occur at any age.

What are the symptoms of an RSV infection?

The symptoms of an RSV infection appear 2 to 8 days after exposure to the virus.

Mild infections are limited to the upper respiratory tract (nose, mouth and throat) and resemble the common cold:

  • blocked and runny nose
  • dry cough
  • moderate temperature.

In most cases these symptoms disappear spontaneously after 2 to 8 days days. 

Symptoms of serious forms of an RSV infection in children

An RSV infection in infants of less than 2 years can develop into pneumonia or bronchiolitis (inflammation of the lung bronchioles, which are the small branches of the airways). 

The symptoms of bronchiolitis are related to the lower respiratory tract:

  • severe cough
  • abundant phlegm
  • breathing difficulties and wheezing (in the case of bronchiolitis)
  • bluish skin
  • dehydration
  • refusal to eat.

Sometimes premature babies and infants show no other respiratory symptoms and the RSV infection can appear in the form of lethargy, feeding difficulties and apnoea (a pause in breathing that lasts at least several seconds).

In the majority of cases the symptoms of bronchiolitis last from 8 to 10 days.

However, parents should carefully monitor for the respiratory signs which might suggest a worsening of the RSV infection and they should be very aware of the risk of dehydration. 

The breathing difficulties of premature babies and small infants often require hospitalisation in intensive care. 

DID YOU KNOW? Wheezing is a characteristic sign of bronchiolitis in infants. The tiny branches of the airways are very fine and get blocked because of the swelling of the mucous membranes.


Sciensano centralises and analyses all data provided by the different partners (network of sentinel laboratories and the National Reference Centre) and in this way is able to follow up the evolution of RSV infections.


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