Most RSV infections look and feel like a common cold and clear up on their own within one to two weeks. The time to be concerned is when symptoms move beyond the nose and throat into the lungs, causing breathing difficulty, persistent high fever, or signs of dehydration. Knowing what to watch for, and when in the illness to watch most closely, can help you tell the difference between a normal course and one that needs medical attention.
How RSV Typically Progresses
After exposure, symptoms usually appear within four to six days. They tend to come on gradually: a runny nose, sneezing, mild cough, and sometimes a low fever. For most children and nearly all healthy adults, this is the entire illness. Symptoms last roughly two to eight days, though a lingering cough can stretch a bit longer.
The critical window is days three through five after symptoms start. This is when RSV symptoms peak and when the infection is most likely to spread from the upper airways down into the lungs. If the illness is going to become serious, this is usually when you’ll see it happen. By day six or seven, most people are clearly improving.
Warning Signs in Babies and Toddlers
Infants are hit hardest by RSV. About 10% of babies under one year old with RSV end up needing hospital care. Premature infants and those with chronic lung disease or congenital heart conditions face even higher odds. The signs that an infant’s infection has become dangerous are mostly about breathing:
- Rapid, shallow breathing that looks different from how your baby normally breathes
- Chest retractions, where the skin between or below the ribs visibly pulls inward with each breath
- Nasal flaring, where the nostrils widen noticeably during breathing
- Wheezing, a high-pitched sound especially on exhale
- Bluish color around the lips, fingernails, or skin, which signals low oxygen
- Unusual lethargy or irritability beyond normal fussiness
- Poor feeding, particularly refusing the breast or bottle
Any blue tint to the skin, difficulty breathing, or a baby who is too tired to eat warrants immediate medical attention. These aren’t “wait and see” symptoms.
Tracking Hydration
Babies who are struggling to breathe often stop eating and drinking enough, and dehydration can become a problem on its own. The clearest way to monitor hydration in an infant is by counting wet diapers. Fewer than six wet diapers in 24 hours signals mild to moderate dehydration. If your baby is only producing one to two wet diapers a day, that’s severe dehydration and needs prompt medical care. A dry mouth, no tears when crying, and a sunken soft spot on the head are additional red flags.
When Fever Becomes a Concern
A low-grade fever is normal with RSV and usually isn’t dangerous on its own. The concern rises when fever is high, persistent, or appears alongside worsening respiratory symptoms. A fever reaching 105°F (40.5°C) or one that lasts more than two days suggests the infection may have reached the lungs or that a secondary bacterial infection is developing. Symptoms lasting beyond 10 days without improvement also warrant a call to your child’s doctor.
For very young infants under three months old, any fever at all during an RSV infection is worth reporting to a pediatrician, since their immune systems are less equipped to fight it off.
When RSV Moves to the Lungs
The shift from a mild upper respiratory infection to something more serious happens when the virus reaches the smaller airways in the lungs. This can cause bronchiolitis (inflammation of those tiny airways) or pneumonia (infection of the lung tissue itself). Both produce overlapping symptoms: rapid breathing, wheezing, and high fever.
Pneumonia tends to bring a few additional signs that set it apart. Coughing up yellow, green, or bloody mucus is more common with pneumonia than with bronchiolitis alone. Chest pain during coughing or breathing is another clue. These symptoms can develop gradually over a few days or appear quite suddenly, sometimes overnight. Either way, they signal that the infection has progressed past what the body can easily handle on its own.
RSV Concerns for Adults
Healthy adults typically experience RSV as nothing more than a bad cold. The risk climbs significantly with age: hospitalization rates for adults 85 and older approach 12%, similar to the rate seen in infants. Adults between 75 and 84 aren’t far behind at roughly 10%.
Beyond age alone, certain conditions make RSV more dangerous for adults. Asthma, COPD, heart failure, diabetes, and a weakened immune system all increase the chance of a mild RSV case turning into pneumonia or triggering a flare of the underlying condition. An older adult with COPD, for example, might find that what seems like a simple cold rapidly worsens their baseline breathing.
Adults should seek care if they experience difficulty breathing, chest pain or pressure, sudden dizziness or confusion, trouble keeping fluids down, or symptoms that are clearly getting worse rather than better after the first week. Confusion in an older adult is an especially important signal, since it can indicate low oxygen levels even before other breathing symptoms become obvious.
Who Is at Highest Risk
Some groups face a disproportionate chance of severe illness and should be monitored more closely from the start of any RSV infection:
- Premature infants, especially those born before 29 weeks
- Babies under 6 months old, whose airways are small and immune defenses are still developing
- Children with chronic lung disease or congenital heart conditions
- Adults 75 and older, particularly those in their mid-80s and beyond
- Anyone with a weakened immune system, whether from medication, cancer treatment, or an underlying condition
- Adults with chronic heart or lung disease, or diabetes
If someone in these groups develops RSV symptoms, the threshold for calling a doctor should be lower. Don’t wait for dramatic warning signs. Even persistent coughing, increased fatigue, or mild breathing changes are worth reporting early.
Vaccines and Prevention
RSV vaccines are now available for two key populations. Adults 75 and older are recommended a single dose, and adults 50 to 74 with increased risk factors are also eligible. The best time to get vaccinated is late summer or early fall, before RSV season picks up, though eligible adults can receive it year-round. It is not an annual vaccine; one dose is currently the recommendation.
For infants, protection comes through a different route. Pregnant individuals can receive a vaccine between 32 and 36 weeks of pregnancy, which passes protective antibodies to the baby and helps shield them during the first six months of life, when they’re most vulnerable.
What to Watch at Home
If you’re caring for someone with RSV at home, the most important thing is tracking the trajectory. Is the person getting a little better each day, or a little worse? Mild RSV follows a predictable arc: symptoms build over the first few days, peak around days three to five, then gradually improve. Any departure from that pattern deserves attention.
Watch breathing rate and effort closely, especially in young children. Count breaths per minute when the child is calm or sleeping. Look at the chest and neck for signs of labored breathing. Listen for new wheezing or a cough that’s suddenly deeper and more frequent. Keep fluids going steadily, offering small amounts frequently if a baby or child isn’t interested in full feedings. If you have a pulse oximeter at home, oxygen readings that consistently dip below 90% indicate the body isn’t getting enough oxygen and the person needs medical evaluation.
RSV is common and usually mild, but it deserves respect at the extremes of age and in anyone with underlying health conditions. The pattern to watch for is simple: symptoms that are getting worse instead of better, breathing that looks effortful, and a body that can’t stay hydrated. Those are the signals that RSV has moved past “just a cold” territory.