Respiratory syncytial virus infection is a common respiratory illness that affects nearly every child before their second birthday, and while most cases feel like a bad cold, some can lead to serious breathing difficulties requiring hospital care.
Understanding RSV Infection
Respiratory syncytial virus, commonly known as RSV, is a virus that infects the nose, throat, and lungs. Despite being so widespread that almost all children catch it before turning two years old, many people only learn about this infection when it affects someone they know. The virus causes infections of the respiratory tract, which includes all the airways we use to breathe.[1]
What makes RSV particularly interesting from a medical standpoint is that getting infected once does not provide lasting protection. The immunity—the body’s defense against infection—that develops after having RSV fades over time, meaning you can catch it again and again throughout your life. Some people even experience two separate RSV infections within a single year. For most adults and older children, repeated infections tend to cause only mild symptoms similar to a common cold. However, the first infection in babies and certain vulnerable groups can be much more serious.[5]
How Common Is RSV?
RSV is remarkably common worldwide. In the United States alone, this virus causes approximately 2.1 million visits to doctors’ offices and between 58,000 and 80,000 hospital admissions among children under five years old each year. For infants under one year old, RSV stands as the leading cause of hospitalization. The numbers are even more striking when looking at the broader picture: roughly 80 percent of children hospitalized with RSV do not have any special risk factors—they are otherwise healthy babies who simply got very sick from this particular virus.[3]
RSV does not only affect young children. Adults also get infected regularly, particularly older adults. Each year, the virus causes an estimated 100,000 to 160,000 hospitalizations in adults who are 60 years and older in the United States. The actual burden across all age groups is likely even higher because many RSV infections go unreported or are mistaken for other respiratory illnesses.[3]
The infection typically follows seasonal patterns. In most parts of the United States and similar climates, RSV season generally begins in the fall and peaks during winter months, usually reaching its highest point in December and January. However, the exact timing and severity can vary from year to year and from one community to another.[2]
What Causes RSV and How Does It Spread?
A virus—specifically the respiratory syncytial virus—causes this infection. It is important to understand that RSV is caused by a virus, not bacteria, which means antibiotics will not help treat it.[5]
RSV spreads very easily from person to person through several routes. When someone who has RSV coughs or sneezes, they release tiny droplets containing the virus into the air. If these droplets land in your eyes, nose, or mouth, you can become infected. You can also catch RSV through direct contact, such as kissing the face of a child who has the infection. Another common way the virus spreads is through contaminated surfaces. If someone with RSV touches a doorknob, toy, or countertop, the virus can remain alive on that hard surface for several hours. When you touch that contaminated surface and then touch your face before washing your hands, the virus can enter your body.[4]
The virus does not survive as long on soft surfaces like tissues and hands, but it can still spread this way. Children often get exposed to RSV outside the home—at school, daycare centers, or during playdates—and then bring the virus home to other family members.[3]
Who Is Most at Risk?
While RSV can infect people of all ages, certain groups face a much higher risk of developing severe illness that requires medical attention or hospitalization. Infants, especially those younger than six months old, are among the most vulnerable. Their immune systems are still developing, and their airways are much smaller than those of older children or adults. When these tiny airways become inflamed and filled with mucus during an RSV infection, breathing becomes very difficult.[1]
Premature infants face even greater risks. Babies born early often have underdeveloped lungs and weaker immune systems, making them particularly susceptible to serious complications from RSV. Similarly, young children under two years old with smaller airways are more likely to become severely ill.[5]
Older adults, particularly those aged 75 and above, also face increased danger from RSV. As we age, our immune system becomes less effective at fighting off infections. Adults over 65 with chronic medical conditions have an especially high risk of severe disease.[3]
People with certain underlying health conditions face higher risks regardless of age. Those with chronic heart disease, including congenital heart disease—heart problems present from birth—are more vulnerable. People with chronic lung conditions such as asthma or chronic obstructive pulmonary disease (COPD)—a group of lung diseases that make breathing difficult—are also at increased risk. Anyone with a weakened immune system, whether from medical conditions like HIV or treatments like chemotherapy, faces greater danger from RSV. Additionally, people with conditions like diabetes or obesity have elevated risk for severe outcomes.[3]
Recognizing the Symptoms
RSV symptoms typically begin to appear about four to six days after someone becomes infected with the virus. The symptoms usually develop gradually over several days rather than all appearing at once. For most people, especially adults and older children, RSV causes symptoms very similar to a common cold.[10]
Common symptoms include a runny or congested nose, coughing, sneezing, and fever. Many people also experience a sore throat, headache, and general tiredness. A decrease in appetite is common, as feeling unwell often makes eating less appealing. These symptoms, while uncomfortable, are generally manageable at home for otherwise healthy individuals.[1]
In very young infants, symptoms may look quite different and can be harder to recognize. Some babies with RSV show only irritability, meaning they seem fussy and difficult to comfort. They may be less active than usual, sleeping more or showing less interest in their surroundings. Decreased activity and feeding problems are warning signs that should prompt parents to contact their healthcare provider. Some infants may have trouble breathing as their only obvious symptom.[4]
When RSV spreads to the lower respiratory tract—the airways deeper in the lungs—it can cause more serious infections. These include pneumonia, which is an infection of the lungs themselves, and bronchiolitis, which is inflammation of the small airways entering the lungs. Signs that the infection has become more severe include a worsening cough that becomes more frequent or sounds different. Wheezing—a high-pitched whistling sound usually heard when breathing out—indicates that the airways have become narrowed. Rapid breathing, difficulty breathing, or long pauses between breaths are serious warning signs.[1]
Certain symptoms require immediate emergency medical attention. If you or your child develops bluish or grayish coloring of the skin, lips, or nails, this indicates dangerously low oxygen levels in the blood. If a child’s chest muscles and skin pull inward with each breath, called retractions, or if their nostrils flare out when breathing, these are signs of severe breathing difficulty. Shortness of breath so severe that someone is gasping, choking, or unable to speak in full sentences requires emergency care.[5]
Preventing RSV Infection
Several strategies can help reduce the spread of RSV and protect vulnerable individuals from infection. Basic infection prevention practices form the foundation of protection. Covering coughs and sneezes, preferably with a tissue or into your elbow rather than your hands, helps prevent spreading virus-containing droplets. Washing hands frequently with soap and water for at least 20 seconds is one of the most effective ways to remove viruses before they can cause infection.[3]
Avoiding close contact with people who are sick helps limit exposure. When you are sick yourself, staying home and away from others prevents spreading the virus to vulnerable individuals. Cleaning and disinfecting frequently touched surfaces like doorknobs, light switches, phones, and toys can eliminate virus particles that might otherwise cause infection. Avoiding touching your face, particularly your eyes, nose, and mouth, prevents viruses on your hands from entering your body.[3]
For newborn babies, especially those born prematurely or with serious health conditions, it is wise to try to keep them away from anyone with cold or flu symptoms. While this is not always possible, limiting exposure during the first few months of life when infants are most vulnerable can make a meaningful difference.[8]
Medical prevention options have expanded significantly in recent years. Vaccines are now available for certain groups. Adults aged 75 and older, as well as adults aged 50 to 74 with certain chronic health conditions like lung or heart disease, weakened immune systems, or who live in nursing homes, can receive an RSV vaccine. These vaccines require only a single lifetime dose. Pregnant people can receive an RSV vaccine between 32 and 36 weeks of pregnancy during RSV season, which helps protect their newborn babies for the first six months of life.[3]
For babies and young children, medicines called monoclonal antibodies—laboratory-made proteins that can help the immune system fight off viruses—are available to help prevent severe RSV illness. These medicines are given as injections and are recommended for infants before or during their first RSV season. While these medicines can help prevent severe disease, they cannot cure or treat children who already have RSV, and they do not prevent infection entirely—they just make illness less severe if infection occurs.[4]
How the Body Responds to RSV
When RSV enters the respiratory system, it begins to infect the cells lining the airways. The virus particularly targets the cells in the nose, throat, and lungs. As the virus multiplies inside these cells, the body’s immune system recognizes the infection and launches a response. This immune response causes many of the symptoms we experience—fever develops as the body raises its temperature to create an environment less favorable to the virus, and inflammation occurs as immune cells rush to the infected areas.[12]
In the airways, infection and inflammation lead to increased production of mucus. This mucus, while part of the body’s defense mechanism to trap and remove the virus, can accumulate and cause congestion and coughing. The inflammation also causes the airways to swell, which narrows the passages through which air flows. In adults and older children with larger airways, this narrowing may cause only mild symptoms. However, in infants with naturally tiny airways, even a small amount of swelling and mucus can create significant breathing problems.[1]
When RSV infection spreads to the lower respiratory tract, it can affect the smaller airways deep in the lungs. Bronchiolitis occurs when these small airways become inflamed and filled with mucus and cellular debris. The inflammation and blockage make it harder for air to flow in and out of the lungs, leading to rapid breathing, wheezing, and in severe cases, respiratory failure where the body cannot get enough oxygen. Some infants may also experience episodes where their breathing pauses for short periods, which can be dangerous.[13]
RSV can also cause damage to the cells lining the airways, which may take weeks to fully heal. This is why some people, especially children, continue to have a cough for several weeks even after the acute infection has resolved. In some cases, particularly severe RSV infection in infancy has been associated with an increased risk of developing asthma or recurrent wheezing later in childhood, though researchers are still working to fully understand this connection.[12]
