RSV typically starts like a common cold, with a runny nose and mild congestion that appear 4 to 6 days after exposure to the virus. Symptoms show up in stages rather than all at once, which is why the earliest signs are easy to dismiss. Understanding the progression helps you recognize when a simple cold might be something more, especially in infants and older adults.
How the Virus Gets In
RSV spreads through respiratory droplets when an infected person coughs or sneezes, but touching contaminated surfaces is also a common route. The virus is surprisingly resilient outside the body. It survives up to 7 hours on hard surfaces like countertops, about 5 hours on rubber gloves, 2 hours on fabric, and roughly 20 minutes on skin. Touching one of these surfaces and then rubbing your eyes, nose, or mouth is all it takes.
Once the virus reaches your airways, two proteins on its surface do the work. One protein latches onto the ciliated cells lining your airways (the cells with tiny hair-like structures that normally sweep mucus and debris out of your lungs). A second protein fuses the virus’s outer layer with your cell membrane, letting the virus slip inside and begin replicating. This fusion protein is unusually self-sufficient. Unlike similar viruses, RSV can infect cells using the fusion protein alone, which partly explains why it spreads so efficiently.
The First Few Days
After exposure, you won’t notice anything for 4 to 6 days while the virus replicates. During this incubation period, you can actually become contagious a day or two before symptoms appear, meaning you may be spreading the virus without knowing you’re sick.
The first symptoms to show up are almost always upper respiratory: a runny nose, sneezing, and mild congestion. A low fever and slight cough often follow within a day or two. Appetite may drop. At this stage, RSV looks identical to a regular cold, and in most healthy older children and adults, that’s all it ever becomes. The whole illness resolves in one to two weeks.
Because these early symptoms are so generic, it’s essentially impossible to distinguish RSV from other respiratory viruses like the flu or COVID-19 based on symptoms alone. Testing is the only way to confirm it.
When It Moves to the Lungs
The critical shift happens when the virus spreads from the nose and throat down into the lower airways. In infants, this progression typically occurs 2 to 3 days after the first cold-like symptoms appear. The cough deepens, breathing becomes faster or more labored, and wheezing may start. This is the point where RSV crosses from a nuisance into something that needs closer attention.
In the lower airways, the virus triggers inflammation and excess mucus production in the small breathing tubes (bronchioles). Because these tubes are already tiny in infants, even modest swelling can significantly restrict airflow. This is what makes RSV more dangerous for babies than for adults, whose larger airways can tolerate the same level of inflammation without as much trouble.
How RSV Starts Differently in Infants
In babies younger than 6 months, the earliest signs of RSV often aren’t respiratory at all. Parents may notice irritability, decreased activity, or a reluctance to eat or drink before any coughing or congestion develops. These behavioral changes can be the first clue that something is off.
One symptom unique to very young infants is apnea, which refers to pauses in breathing lasting longer than 10 seconds. This can occur early in the illness and sometimes before other respiratory symptoms become obvious. It’s one of the reasons RSV in newborns requires a different level of vigilance than RSV in older children. A baby who seems unusually fussy, is feeding poorly, or has noticeable pauses in breathing warrants prompt medical evaluation, even without a cough.
How RSV Starts in Adults
For most healthy adults, RSV begins and ends as a mild cold. The runny nose, congestion, cough, and low-grade fever follow the same general pattern as in children, and the illness typically clears within a week or two without complications. Many adults with RSV never realize they have anything other than a standard cold.
The risk changes for adults over 65 and those with chronic heart or lung conditions or weakened immune systems. In these groups, the virus is more likely to progress to the lower airways, causing persistent cough, wheezing, and shortness of breath. The initial onset still looks like a cold, but the illness can deepen rather than improve after the first few days.
Contagious Period
People with RSV are typically contagious for 3 to 8 days, starting a day or two before symptoms even begin. This pre-symptomatic spread is a major reason RSV moves so quickly through households and daycare settings. By the time a child develops a runny nose, they may have already been shedding the virus for 48 hours.
Some groups remain contagious much longer. Infants and people with weakened immune systems can continue spreading RSV for 4 weeks or more, even after their symptoms have resolved. This extended shedding period makes containment difficult in hospitals and care facilities, and it’s why RSV outbreaks in these settings can be persistent.