RSV (respiratory syncytial virus) typically causes cold-like symptoms: runny nose, coughing, sneezing, fever, and decreased appetite. Symptoms usually appear 4 to 6 days after exposure and resolve on their own within a week or two. For most healthy older children and adults, RSV feels like an ordinary cold. But in infants, older adults, and people with weakened immune systems, the same virus can cause serious breathing problems that require hospitalization.
During the 2024–2025 respiratory season, RSV was linked to an estimated 190,000 to 350,000 hospitalizations and 10,000 to 23,000 deaths in the United States. Understanding which symptoms are routine and which signal trouble makes a real difference in knowing when to act.
How RSV Causes Breathing Problems
RSV targets the small tubes that carry air in and out of the lungs, called bronchioles. When the virus infects these airways, they swell and become inflamed, and excess mucus builds up inside them. That combination partially or completely blocks airflow, which is why wheezing (a whistling sound when breathing out) is one of RSV’s hallmark symptoms. In older kids and adults, the larger airways handle this swelling without much difficulty. In babies, whose airways are already tiny, even mild swelling can make breathing significantly harder.
Symptoms in Infants and Young Children
RSV is most dangerous for babies under 12 months old. Hospitalization rates during the 2024–2025 season were highest in this age group, at roughly 1,050 to 1,117 per 100,000 infants. Children ages 1 to 2 were the next most affected group.
Early symptoms in babies look like a typical cold: runny nose, coughing, sneezing, fussiness, and reduced feeding. Over the next few days, symptoms can progress to involve the lower airways, and that’s when things become more concerning. Signs to watch for include:
- Wheezing: a high-pitched whistling sound during breathing
- Rapid breathing: noticeably faster than normal for your child’s age
- Nasal flaring: nostrils spreading wide with each breath as the body works harder to pull in air
- Chest retractions: the skin between the ribs or below the ribcage visibly pulls inward with each breath, sometimes described as the chest “caving in”
- Belly breathing: the stomach moves up and down more than the chest during breathing
In very young infants under 6 months, RSV can also cause apnea, which means pauses in breathing lasting longer than 10 seconds. This is one of the most alarming symptoms and requires immediate medical attention. Babies in this age group may also show fewer obvious cold symptoms beforehand, making apnea sometimes the first noticeable sign of trouble.
Decreased feeding is another important warning sign in infants. Babies who are struggling to breathe often can’t coordinate sucking and swallowing, so they eat less. If your baby is refusing bottles or breastfeeding sessions and producing fewer wet diapers than usual, that’s a signal the illness is affecting them more seriously.
Symptoms in Adults
When healthy adults catch RSV, it typically feels like a standard cold: congestion, sore throat, cough, mild headache, fatigue, and sometimes a low-grade fever. Most people recover without ever knowing they had RSV rather than another respiratory virus.
The picture changes for adults 75 and older, people with chronic lung diseases like COPD or asthma, those with heart failure, and anyone with a weakened immune system. In these groups, RSV can progress to pneumonia. It can also trigger flare-ups of existing conditions, making COPD or heart failure suddenly worse. Adults living in nursing homes face elevated risk because of close quarters and often multiple underlying health conditions.
Warning signs that RSV has moved beyond a simple cold in adults include difficulty breathing, chest pain or pressure, trouble eating or drinking enough fluids, sudden dizziness or confusion, and symptoms that seem to improve but then worsen again.
RSV Timeline: What to Expect Day by Day
After exposure, you won’t notice anything for 4 to 6 days while the virus incubates. Symptoms then typically start with upper respiratory signs: runny nose, mild cough, and possibly a low fever. Over the next 2 to 3 days, the cough usually worsens and may move into the chest. If the illness is going to become severe, days 3 through 5 of symptoms are generally when breathing difficulties peak.
Most RSV infections clear up within one to two weeks. The cough can linger for several weeks even after the infection itself has resolved. In children who develop wheezing, it may take a few extra days for the airway swelling to fully settle down.
How RSV Differs From a Cold or Flu
The early symptoms of RSV are nearly identical to a common cold, which is why it’s hard to distinguish without testing. Two features that lean toward RSV rather than a generic cold are prominent wheezing and visible breathing difficulty, especially in children under 2. A regular cold rarely causes the kind of lower airway involvement that makes the chest pull in with each breath.
Compared to the flu, RSV tends to start more gradually. Influenza often hits suddenly with high fever, body aches, and exhaustion. RSV builds over a few days from a runny nose to a deeper cough. That said, the overlap is significant enough that a lab test is the only reliable way to confirm which virus is responsible. The most accurate option is a PCR test, which detects the virus’s genetic material from a nasal swab. Rapid antigen tests are also available and return results faster, though they’re somewhat less sensitive.
When Symptoms Become an Emergency
In children, seek immediate care if you notice pauses in breathing, bluish color around the lips or fingernails, chest retractions that are getting more pronounced, or if your child seems unusually lethargic or difficult to wake. A baby who refuses to eat or drink and is producing significantly fewer wet diapers needs evaluation promptly.
In adults, difficulty breathing at rest, persistent chest pain or pressure, confusion or sudden dizziness, and an inability to keep fluids down all warrant urgent medical attention. Symptoms that improve for a day or two and then sharply worsen can indicate a secondary infection like bacterial pneumonia developing on top of the RSV illness.