RSV (respiratory syncytial virus) is a common respiratory virus that infects the lungs and airways, and yes, it is highly contagious. Most people recover within a week or two with mild cold-like symptoms, but RSV can cause serious illness in infants, older adults, and anyone with a weakened immune system.
What RSV Does to Your Airways
RSV belongs to a virus family called Pneumoviridae, which targets the respiratory tract. In most healthy older children and adults, the virus stays in the upper airways, causing symptoms no worse than a typical cold: runny nose, sore throat, cough, headache, fatigue, and sometimes a low fever.
The virus becomes dangerous when it moves deeper into the lungs. In infants and high-risk adults, RSV can inflame the small airways (bronchiolitis) or infect the lung tissue itself (pneumonia). Both conditions make it harder to get enough oxygen. RSV can also worsen existing lung and heart conditions like asthma, COPD, and congestive heart failure.
How RSV Spreads
RSV spreads through respiratory droplets when an infected person coughs or sneezes, through direct contact like kissing a child’s face, and by touching contaminated surfaces and then touching your eyes, nose, or mouth. It’s an efficient spreader: a person with RSV is typically contagious for 3 to 8 days and can start spreading the virus a day or two before any symptoms appear. That pre-symptomatic window is part of what makes RSV so hard to contain, especially in daycare settings and households with multiple children.
Infants and people with weakened immune systems can shed the virus for 4 weeks or longer, even after their symptoms have cleared. This is why RSV moves so easily through families. A parent or older sibling might feel fine and still be passing the virus to a baby at home.
Symptoms in Babies vs. Adults
The gap between how RSV looks in a baby and how it looks in an adult is significant, which is why many parents don’t realize the virus has entered their household until the baby gets sick.
Adults who catch RSV usually experience mild upper respiratory symptoms: a runny nose, cough, sore throat, headache, and fatigue. Many adults mistake it for a regular cold and never get tested. Adults over 50, particularly those over 75 or with chronic health conditions, face a higher risk of the infection reaching the lungs.
In infants and young children, the first signs are often a runny nose and decreased appetite. A cough typically develops 1 to 3 days later, followed by sneezing, fever, and wheezing. Very young infants may not cough much at all. Instead, they may become unusually irritable, lethargic, or have brief pauses in breathing (apnea). These subtler signs are easy to miss.
Warning Signs That Need Emergency Care
Most RSV infections resolve on their own, but certain symptoms signal that breathing is becoming dangerously compromised. Watch for:
- Skin pulling inward between the ribs with each breath (called retractions)
- Nostrils flaring wider with each breath
- Fast, shallow, or irregular breathing, or pauses in breathing
- Wheezing or noisy breathing that worsens
- Bluish or grayish color on the skin, lips, or fingernails
Any of these signs in a baby or young child warrants an emergency room visit. In a hospital setting, treatment focuses on supporting breathing and hydration: supplemental oxygen, IV fluids if the child can’t feed, and in severe cases, a ventilator.
Incubation and Timeline
After exposure, symptoms typically appear within 4 to 6 days. The illness usually runs its course in 1 to 2 weeks for most people. In infants, the worst days tend to fall around days 3 to 5 of symptoms, when congestion and breathing difficulty peak. Mild coughing can linger for a few weeks after the rest of the symptoms resolve.
Who Is Most at Risk
Nearly all children catch RSV at least once before their second birthday. For most, it’s an uncomfortable but manageable illness. The groups at highest risk for severe disease include premature infants, babies under 6 months old, children with congenital heart or lung conditions, and adults over 75. Anyone with a suppressed immune system, whether from medication or an underlying condition, also faces greater danger.
Recent data illustrates just how common severe RSV is in young children. During the 2024-25 season, the hospitalization rate among infants under 8 months was approximately 8.5 per 1,000 children, a meaningful number even after a significant drop from previous years.
Vaccines and Prevention
RSV vaccines are now available for two main groups. For adults, the CDC recommends a single dose for everyone 75 and older, and for adults 50 to 74 who are at increased risk of severe illness. Adults 18 to 49 with certain risk factors are also eligible. Three vaccines are currently approved for adults, with no preference among them. This is not an annual shot; one dose is considered complete for now. The best time to get vaccinated is late summer or early fall (August through October in most of the U.S.), just before RSV season peaks.
For infants, protection comes through a different route. Babies can receive an antibody product that provides passive immunity during their most vulnerable months. Maternal vaccination during pregnancy is another option, giving the baby protective antibodies at birth. These prevention tools have had a measurable impact: hospitalization rates among infants under 8 months dropped by roughly 43% in the 2024-25 season compared to pre-pandemic baselines, with the largest reductions seen in the youngest babies under 3 months old.
Beyond vaccines, basic hygiene measures remain the simplest way to reduce spread. Washing hands frequently, avoiding close contact with sick individuals, and keeping surfaces clean all help, especially during peak RSV season from late fall through early spring. If you have a cold and there’s a baby in the household, wearing a mask and avoiding kissing the baby’s face can lower transmission risk during the days you’re most contagious.