RSV (respiratory syncytial virus) causes cold-like symptoms in most people: runny nose, coughing, sneezing, fever, and decreased appetite. Symptoms typically appear 4 to 6 days after infection and show up in stages rather than all at once. Most infections clear on their own within one to two weeks, but RSV can become serious in infants, older adults, and people with weakened immune systems.
Symptoms in Babies and Young Children
Nearly all children catch RSV by age two, and for most of them it looks like an ordinary cold. A runny nose and mild cough come first, sometimes with a low fever and fussiness. Appetite often drops, and younger babies may seem unusually sleepy or irritable.
In more severe cases, the virus moves deeper into the lungs and causes bronchiolitis (inflammation of the small airways) or pneumonia. When that happens, you may notice wheezing, a high-pitched sound when your child breathes out. Breathing can become visibly labored: the skin between the ribs or below the ribcage pulls inward with each breath, the nostrils flare, and the belly moves up and down more than normal. Some very young infants develop brief pauses in breathing.
Infants under 12 months are hospitalized for RSV at a rate of roughly 1,100 per 100,000, making it one of the leading causes of infant hospitalization in the U.S. Children aged 12 to 23 months are the next most affected group, hospitalized at about 770 per 100,000. Premature babies and those born with heart or lung conditions face the highest risk of severe illness.
Symptoms in Adults
Adults with RSV typically experience mild cold symptoms: congestion, sore throat, a dry cough, headache, and low-grade fever. Many brush it off as a regular cold and recover without any specific treatment. The illness generally follows the same one-to-two-week timeline as in children.
For some adults, though, RSV progresses to pneumonia. It can also flare up existing conditions like asthma, COPD, and heart failure. Adults 75 and older, those with chronic heart or lung disease, people with weakened immune systems, and residents of nursing homes face the greatest risk. During the 2024-2025 season, adults 75 and older were hospitalized at a rate of about 427 per 100,000, and over 82% of recorded RSV deaths occurred in people 65 and older.
How Symptoms Progress Day by Day
RSV doesn’t hit all at once. The typical pattern looks something like this:
- Days 1 to 3: Runny nose, sneezing, mild cough, possibly a low fever. At this stage it’s indistinguishable from a common cold.
- Days 3 to 5: Coughing may intensify. In babies and high-risk individuals, wheezing or faster breathing can develop as the virus reaches the lower airways.
- Days 5 to 7: Symptoms typically peak. This is when breathing difficulty, if it’s going to happen, becomes most apparent.
- Week 2: Most people improve steadily. A lingering cough can stick around for a few weeks even after the infection clears.
Warning Signs of Severe RSV
Knowing what mild RSV looks like is helpful, but recognizing severe illness matters more. In infants, the clearest red flags are visible effort to breathe. Watch for the chest pulling inward with each breath, flared nostrils, and grunting sounds. A breathing rate above 60 breaths per minute in a baby is a concern. Bluish or grayish color around the lips or fingernails signals that oxygen levels have dropped.
Refusal to eat or drink is another important warning sign in babies, partly because congestion makes it hard to nurse or take a bottle while breathing, and dehydration can develop quickly. Fewer wet diapers than usual, no tears when crying, and unusual sleepiness or difficulty waking are signs of dehydration.
In older adults, watch for shortness of breath during normal activities, persistent chest tightness, confusion or unusual drowsiness, and a fever that won’t come down. These can signal pneumonia or worsening of an underlying condition.
RSV vs. Flu vs. COVID-19
RSV, influenza, and COVID-19 share many symptoms, including fever, cough, and shortness of breath. You cannot reliably tell them apart based on symptoms alone. A few patterns can offer clues, though they’re not definitive. RSV tends to start with heavy nasal congestion and is more likely to cause wheezing, especially in young children. The flu often comes on suddenly with body aches, high fever, and intense fatigue. COVID-19 is more commonly associated with loss of taste or smell, though that symptom has become less frequent with newer variants.
The only reliable way to know which virus you’re dealing with is a diagnostic test. PCR-based tests are the most accurate and can detect RSV, flu, and COVID-19 from a single nasal swab. Rapid antigen tests for RSV are also available and give faster results, though they’re somewhat less sensitive than PCR.
Long-Term Effects in Children
For most kids, RSV comes and goes without lasting impact. But a growing body of evidence links RSV infection during infancy to a higher risk of developing asthma later in childhood. A large study tracking nearly 2,000 infants from birth found that children who were not infected with RSV during their first year of life had a 26% lower risk of asthma by age five compared to those who were infected. The connection is strongest in children whose RSV infection was severe enough to cause wheezing or require medical attention. This doesn’t mean RSV causes asthma in every child, but it does appear to be one contributing factor, particularly in kids who may already have a genetic predisposition.
Who Faces the Greatest Risk
RSV is most dangerous at the extremes of age and in people whose immune defenses are compromised. The highest-risk groups include:
- Premature infants and babies under 6 months old
- Children under 2 with congenital heart disease or chronic lung conditions
- Adults 75 and older
- People with weakened immune systems from conditions like organ transplant, chemotherapy, or HIV
- Adults with chronic heart or lung disease, including COPD and heart failure
- Nursing home residents, where close quarters and shared spaces make transmission easy
During the 2024-2025 respiratory season, RSV was associated with an estimated 190,000 to 350,000 hospitalizations and 10,000 to 23,000 deaths in the United States. The vast majority of deaths occurred in older adults, but even among younger age groups, people with underlying conditions faced disproportionate risk.