Health A-Z

Medical Content Created by the Faculty of the Harvard Medical School


What Is It?

Respiratory syncytial virus (RSV) is one of the many viruses that cause the common cold and infections in the upper parts of the respiratory tract. RSV also can cause infection in the lower respiratory tract, such as pneumonia in the lung tissue and bronchiolitis inside the smallest airways (bronchioles) in the lungs.

RSV is spread in secretions when someone with it coughs or sneezes. RSV also can be carried on unwashed hands and on contaminated objects, such as dirty tissues, doorknobs and desk tops. It typically enters the body through the eyes, nose or mouth when someone with contaminated fingers touches his or her face or eyes or breathes in droplets.

People who have the greatest risk of serious illness from RSV include:

  • Infants, especially those who were born early (premature)

  • The elderly

  • People of any age with certain types of heart disease, chronic lung disease or weakened immune systems

The highest rates of serious childhood RSV illness occur in infants under 6 months old. Almost all children have been exposed to RSV by the age of 2. Most do not become dangerously ill. Getting RSV more than once can happen, but infections that follow the first one generally are mild.

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From Health A-Z, Harvard Health Publications. Copyright 2007 by the President and Fellows of Harvard College. All rights reserved. Written permission is required to reproduce, in any manner, in whole or in part, the material contained herein. To make a reprint request, contact Harvard Health Publications. Used with permission of StayWell.

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