RSV (respiratory syncytial virus) often starts looking exactly like a common cold, with a runny nose and mild cough. The key difference is what happens over the next few days: RSV symptoms can worsen rather than improve, progressing to wheezing, difficulty breathing, and trouble feeding. Because early RSV symptoms overlap so heavily with other respiratory viruses, the signs you’re really watching for are the ones that emerge on days three through five of the illness.
Early Symptoms That Signal RSV
The first signs of RSV in a baby are easy to mistake for an ordinary cold. You’ll typically notice a runny nose, a new cough, and your baby eating or drinking less than usual. A low-grade fever is common. At this stage, there’s genuinely no way to tell RSV apart from a cold, the flu, or even COVID just by looking at your baby. The CDC notes that RSV symptoms are not specific enough to distinguish from other respiratory viruses without testing.
What sets RSV apart is the trajectory. A regular cold tends to plateau and slowly get better. With RSV, symptoms often intensify a few days in. That mild cough may progress to wheezing, a whistling sound when your baby breathes out. Your baby may start breathing faster or seem to be working harder to get air. This escalation pattern, where things get noticeably worse around day three to five, is the hallmark parents should watch for.
Breathing Signs That Mean Trouble
The most important thing you can learn as a parent is what respiratory distress looks like in a baby, because babies can’t tell you they’re struggling to breathe. There are three visible signs to check for:
- Chest retractions: The skin between or below your baby’s ribs sucks inward with each breath, creating a visible “caving in” pattern. Pull up your baby’s shirt and watch their chest and belly as they breathe.
- Nasal flaring: Your baby’s nostrils spread wide open with each breath. This means they’re using extra effort just to pull in enough air.
- Rapid, shallow breathing: Breaths become noticeably fast and short. In infants, a breathing rate over 60 breaths per minute is abnormally fast. You can count breaths for 15 seconds and multiply by four.
A blue or grayish tint to the lips, mouth, or fingernails signals that your baby isn’t getting enough oxygen. This is an emergency. So are pauses in breathing lasting longer than 10 seconds, which can happen in very young infants with RSV and may occur even before other symptoms become severe. If you see any of these signs, go to the emergency room immediately.
Feeding and Hydration Clues
Babies with RSV often refuse to eat because breathing through a stuffy nose while sucking on a bottle or breast is genuinely difficult. A slight dip in appetite is expected with any cold, but with RSV, the feeding drop can become significant enough to cause dehydration.
Track wet diapers. A healthy baby produces at least six wet diapers in 24 hours. Fewer than six suggests mild to moderate dehydration. If your baby is down to only one or two wet diapers a day, that’s severe dehydration and needs urgent medical attention. Other dehydration signs include no tears when crying, a dry mouth, and a sunken soft spot on the top of the head.
How Doctors Confirm RSV
If your pediatrician suspects RSV, they can confirm it with a test. The two main options are a PCR test (highly sensitive, same type used for COVID testing) and a rapid antigen test (less sensitive but faster results). Both involve a nasal swab. In many cases, though, doctors diagnose RSV based on symptoms, the time of year, and a physical exam without ordering a test, because the treatment approach for mild RSV is the same regardless of the specific virus.
Testing matters more when a baby is sick enough to need hospital care, since confirming the virus helps guide decisions about isolation and monitoring.
What RSV Recovery Looks Like
Most babies with RSV recover at home within one to two weeks. The fever, if present, usually resolves within the first few days. The cough tends to linger longest, sometimes persisting for two to three weeks even after your baby is clearly improving overall. The critical window is typically days three through five of the illness, when symptoms peak. If your baby gets through that stretch without developing significant breathing difficulty, the trajectory is usually toward recovery.
During that window, suctioning your baby’s nose before feedings can make a real difference. Use a bulb syringe or a nasal aspirator to clear mucus so your baby can breathe while eating. A cool-mist humidifier in the room and keeping your baby upright after feedings also help. There’s no medication that treats RSV itself in otherwise healthy babies. The goal is supporting your baby’s breathing and hydration while their immune system clears the virus.
Which Babies Face the Highest Risk
RSV is most dangerous for babies under 6 months old, premature infants, and children with chronic lung conditions or congenital heart disease. These babies are more likely to develop bronchiolitis, an inflammation of the small airways in the lungs, or pneumonia. They’re also more likely to need hospitalization for supplemental oxygen or IV fluids.
If your baby falls into a high-risk category, a lower threshold for calling the pediatrician makes sense. Don’t wait for dramatic breathing changes. Even persistent feeding refusal or increased fussiness with mild breathing changes warrants a call.
Prevention With RSV Antibodies
A preventive antibody called nirsevimab is now available and recommended for all infants under 8 months old entering their first RSV season (typically October through March in most of the U.S.), provided their mother didn’t receive the RSV vaccine during pregnancy at least 14 days before delivery. This isn’t a vaccine. It’s a single injection of ready-made antibodies that provides protection for about five months.
Babies aged 8 to 19 months who are at high risk, including those with chronic lung disease, severe immune deficiency, or cystic fibrosis with significant lung involvement, are recommended to receive the antibody before their second RSV season as well. American Indian and Alaska Native children in this age range are also eligible due to higher rates of severe RSV in these communities.
If the mother received an RSV vaccine during pregnancy at least two weeks before delivery, the baby generally doesn’t need the antibody injection, since protective antibodies were already passed through the placenta.