By their second birthday, nearly all children in the United States will have had respiratory syncytial virus (RSV). This highly contagious virus causes inflammation of the respiratory tract, usually resulting in cold-like symptoms.

Most kids (and adults, who can get it, too) with an RSV infection recover within a week or two, but it can be serious for those without strong immune systems, including infants and older adults, and for them it can be serious. RSV is the most common cause of bronchiolitis (inflammation of the small airways in the lungs) and pneumonia (a lung infection) in children younger than 1 in the United States.

“The vast majority of kids who get RSV appear to have nothing worse than a simple cold, and never have to be hospitalized,” says Magna Dias, MD, a Yale Medicine pediatric hospitalist (a physician who only sees patients in the hospital). “Some kids may get an ear infection or have a fever with it, so it’s important to have your pediatrician evaluate your child if you have any concerns. And good handwashing or using hand sanitizer will stop it from spreading.”

In mild cases of RSV, inflammation is limited to the upper respiratory tract (the nose and throat), causing a runny nose and nasal congestion. “The hallmark of RSV is mucus production that causes you to blow your nose more frequently,” Dr. Dias says.

Other symptoms include a slight cough, a decrease in appetite, and low-grade fever. More serious RSV infections eventually reach down into the lower respiratory tract (bronchial tubes and lungs). A sign that the infection is worsening is when symptoms get more severe (coughing turning into wheezing, for example).

The runny nose and fever typically begin (then worsen and peak) three to five days after the infection starts. For some, those may be the only symptoms. But roughly half of all children who are infected for the first time experience the later-stage (and more intense) coughing and wheezing symptoms.

This can be serious for infants younger than 6 months. “For little babies who get RSV, having that much mucus obstructs their tiny nasal passages and their airways. This can create difficulty in their breathing, and sometimes their noses are so congested they have trouble breathing through their noses. Of course, they are going to choose to breathe [through the mouth] over eating, and that can lead to dehydration [loss of body fluids] and needing IV fluids,” says Dr. Dias.

RSV is very contagious. It can spread through the droplets released into the air when an infected person coughs or sneezes, or if you touch a contaminated surface, such as counters or doorknobs (where it can live for hours), then touch your nose, eyes, or mouth without washing or sanitizing your hands. It can also spread through direct contact (kissing the face of a child with RSV, for example).

People with RSV are contagious for three to eight days after exposure. But because their immune systems aren’t as good at eliminating the virus, some infants and others with weakened immune systems are contagious for as long as four weeks, even after they no longer have symptoms.

In the U.S., RSV infections are most common during the fall, winter, and spring seasons.

People of any age can get an RSV infection, but previous exposure tends to reduce the severity of symptoms. Here is a list of those with the highest risk of becoming seriously ill from RSV:

• Premature infants
• Very young children (under 6 months)
• Young children (under age 2) with congenital heart or chronic lung disease including asthma
• Young children and adults with weakened immune systems (from illness or medical treatments)
• Children with neuromuscular disorders that make it difficult for them to swallow or clear mucus secretions
• Older adults, in particular those with heart or lung disease

Generally, RSV is diagnosed by a medical professional, based on symptoms and a physical exam.

Your doctor will listen to your child’s lungs with a stethoscope to check for signs of pneumonia or bronchiolitis. RSV can be confirmed with lab tests using a nasal mucus swab, but testing will only be done if it will affect the treatment plan, explains Dr. Dias.

“Most of the time, as with a cold, knowing it is RSV will not make a difference in our care, because the only real treatment for it is supportive care,” she says.

There is no specific treatment for RSV infections. In most cases, RSV infections—especially in healthy children and adults—will clear up within a week or two. Discomfort and fever can be treated with over-the-counter medications such as ibuprofen or acetaminophen. It’s also important to drink plenty of fluids to prevent dehydration.

A person with RSV (especially an infant younger than 6 months or an older adult) may need to be hospitalized if they become dehydrated or have ear pain or trouble breathing, which could be signs of a secondary infection such as an ear infection or pneumonia. Signs of dehydration in babies and young children include a dry mouth and tongue, crying without tears, lethargy, and dry diapers for eight hours or longer. Your child’s doctor will evaluate your child and recommend hospitalization, if necessary.

In the hospital, treatments may include intravenous fluids, or in severe cases, oxygen therapy or mechanical ventilation (having a breathing tube inserted through the mouth and down the airway).

One of the most effective ways to prevent an RSV infection is to practice good hand hygiene. Wash and scrub your hands with water and soap regularly, and especially before holding your baby. Encourage older children and other caregivers to do the same. You can also limit your baby’s exposure to crowded places like shopping centers, where RSV may be prevalent, especially in the winter and spring.

If you have RSV (or any cold symptoms), reduce contagion by covering your mouth and nose when you cough and sneeze with either your shirt sleeve or a tissue (not your hands).

You should avoid close contact (kissing, shaking hands, sharing utensils and cups) with others, especially young children. And disinfect contaminated surfaces—everything from doorknobs to countertops. A medication called palivizumab (brand name Synagis®) may be given (as a shot) to prevent severe lower respiratory tract infection in children and infants who are considered at high risk of RSV disease. Palivizumab is a type of medication known as a monoclonal antibody. It contains laboratory-produced antibodies that target RSV, helping the immune system better fight off the virus. The shot does not improve symptoms for kids already sick with RSV disease, nor does it prevent infection with RSV.

“You need to get the shot every month during the season RSV is active in the community,” Dr. Dias explains. “For our high-risk kids, including babies born extremely prematurely, we will give it to them for their first year of life.”

In July 2023, the Food and Drug Administration (FDA) approved another monocolonal antibody called nirsevimab (brand name Beyfortus™). Nirsevimab is given as a single injection and provides at least five months of protection against severe RSV disease, which is the typical length of an RSV season. The Centers for Disease Control and Prevention (CDC) recommends that all infants 8 months of age or younger who are born during an RSV season or entering their first RSV season receive one dose of nirsevimab. The health agency also recommends that some children aged eight to 19 months who are at increased risk for severe RSV disease be given an additional dose at the start of their second RSV season.

For people ages 60 and older, two vaccines—one called Arexvy and the other Abrysvo™—against RSV are available. The two vaccines were approved by the FDA in May 2023 and recommended by the CDC in June 2023 for prevention of lower respiratory tract disease due to RSV infection. In clinical trials, Arexvy had an 82.6% efficacy in preventing symptomatic lower respiratory disease associated with RSV in the first RSV season, while Abrysvo had an efficacy of 88.9% in the first season. Both vaccines are given as a single dose and can be received at the same time as other vaccines.