RSV (respiratory syncytial virus) typically takes four to six days to show up after exposure. This window, called the incubation period, means you or your child could be infected and feel completely fine for nearly a week before the first symptoms appear. Both the CDC and Mayo Clinic confirm this four-to-six-day range.
What the First Symptoms Look Like
When RSV does appear, it initially looks a lot like a common cold. The earliest signs include a runny nose, sore throat, headache, and a low-grade fever. In young children, you might also notice a decrease in appetite, irritability, or a mild cough. At this stage, there’s nothing obvious that screams “this is RSV” rather than an ordinary virus.
One early clue that can set RSV apart from a typical cold is wheezing, a whistling sound during breathing. This is common with RSV but unusual with a mild cold. The other distinguishing pattern is the direction symptoms move: a cold generally improves steadily after the first few days, while RSV symptoms tend to get worse before they get better.
How Symptoms Progress Over Time
RSV follows a fairly predictable arc. After those first cold-like symptoms appear, the illness intensifies. Symptoms are typically at their worst on days three through five of the illness. This is when coughing deepens, breathing may become more labored, and wheezing is most noticeable. For most people, the entire illness lasts seven to 14 days.
In infants and young children, what starts as mild congestion and a runny nose can shift into something more serious within just a few days. RSV can progress to bronchiolitis (inflammation of the small airways in the lungs) or pneumonia. The CDC notes that RSV may not look severe when it first starts but can worsen a few days into the illness. This is why close monitoring matters, especially in babies under 12 months old. Watch for rapid breathing, flaring nostrils, the skin pulling in between the ribs with each breath, or a bluish tint around the lips.
When You’re Contagious
You can actually spread RSV before you know you have it. People become contagious a day or two before symptoms appear, which means the virus can circulate through a household or daycare before anyone realizes someone is sick. Once symptoms start, most people remain contagious for three to eight days.
There’s an important exception for certain groups. Babies and people with weakened immune systems can continue shedding the virus for up to four weeks after their symptoms resolve. This extended contagious window is one reason RSV spreads so efficiently in childcare settings and hospital environments.
When to Test for RSV
If you suspect RSV after a known exposure, testing too early can give you a false negative. The virus needs time to multiply to detectable levels. Rapid RSV tests work best in the first few days after symptoms begin, not before. So the practical testing window opens once you or your child actually develops symptoms, ideally within the first two to three symptomatic days.
A healthcare provider can confirm RSV with a nasal swab or, in some cases, a blood test. Testing is most commonly done for infants, older adults, and people with underlying health conditions, since the result can influence treatment decisions. For otherwise healthy adults, RSV testing is usually reserved for cases where symptoms aren’t improving on the expected timeline.
RSV in Adults vs. Children
The incubation period is the same regardless of age: four to six days. But how the illness plays out differs significantly. Healthy adults usually experience RSV as a bad cold that resolves within one to two weeks. The symptoms stay in the upper respiratory tract, and most adults never realize they had RSV rather than a regular cold.
Children under two, especially premature infants and those with heart or lung conditions, face a higher risk of the infection moving into the lower airways. This is when RSV becomes more than a cold. Older adults (65 and up) and adults with chronic lung disease or compromised immune systems also face elevated risks of severe illness, including pneumonia.
Timeline at a Glance
- Day 0: Exposure to RSV through respiratory droplets or contaminated surfaces
- Days 1 to 3 after exposure: No symptoms, but the virus is replicating
- Days 4 to 6 after exposure: First symptoms appear (runny nose, mild cough, low fever)
- Days 3 to 5 of illness: Symptoms peak in severity
- Days 7 to 14 of illness: Gradual recovery for most people
The gap between exposure and symptoms is the trickiest part of RSV. You can be contagious before you know you’re sick, and the virus can spread through a family in overlapping waves as each person hits their own four-to-six-day incubation window.