RSV, or respiratory syncytial virus, is a common respiratory virus that infects the nose, throat, and lungs. Nearly every child catches it by age two, and most recover like they would from a cold. But RSV can cause serious illness in infants, young children, and older adults. During the 2024–2025 season alone, it was linked to an estimated 190,000 to 350,000 hospitalizations and 10,000 to 23,000 deaths in the United States.
How RSV Infects the Airways
RSV belongs to a family of viruses called Pneumoviridae, and it comes in two subtypes (A and B) that circulate together during seasonal outbreaks. The virus first takes hold in the lining of the nose and throat. In mild cases, it stays there and causes cold-like symptoms. But RSV can spread rapidly downward through the airways, reaching the smallest branches of the lungs called bronchioles. That’s where the virus replicates most efficiently and where the real damage happens.
When RSV reaches the bronchioles, it kills cells lining those tiny airways. The immune system responds by flooding the area with inflammatory cells, which causes swelling of the airway walls. At the same time, mucus production ramps up and thickens, while the tiny hair-like structures that normally sweep mucus out of the lungs are destroyed. The combination of swelling, thick mucus, and dead cell debris plugs the airways. This is what makes breathing difficult, especially in infants whose airways are already very small. Much of the breathing difficulty actually comes from the body’s own immune response rather than direct damage from the virus itself.
Symptoms in Children and Adults
Symptoms usually appear four to six days after infection. They tend to show up in stages rather than all at once: a runny nose first, followed by coughing, sneezing, decreased appetite, and sometimes fever. In older children and healthy adults, this looks and feels like an ordinary cold and clears up on its own within a week or two.
Very young infants can be harder to read. Their only symptoms may be irritability, decreased activity, and noticeable breathing difficulties. Parents might notice flared nostrils, rapid breathing, or the skin pulling in between the ribs with each breath. These are signs the baby is working harder than normal to get air in.
When the virus reaches the lower lungs, wheezing becomes the hallmark symptom. A child might develop bronchiolitis (inflammation of the small airways) or pneumonia. Work of breathing increases visibly as the body recruits extra muscles in the neck, chest, and belly to push air through obstructed passages.
Who Gets Hit Hardest
Hospitalization rates tell the story clearly. Infants under 12 months are hospitalized at a rate of roughly 1,050 to 1,117 per 100,000, making them the most vulnerable group by far. Children aged 12 to 23 months follow at about 648 to 771 per 100,000. Among older adults, those 75 and above are hospitalized at a rate of roughly 427 per 100,000.
Deaths skew heavily toward older adults. Of RSV-associated deaths recorded during the 2024–2025 season, 82% occurred in adults 65 and older. Children and adolescents accounted for less than 5% of deaths, though the individual tragedies in that group drive much of the public health effort around infant protection.
How RSV Differs From the Flu and COVID-19
RSV, influenza, and COVID-19 share overlapping symptoms: fever, cough, congestion, and sometimes shortness of breath. You cannot reliably tell them apart based on symptoms alone. The main clinical distinction is that RSV is far more likely to cause wheezing and bronchiolitis in young children, while the flu tends to hit with more sudden body aches and high fevers. COVID-19 can cause loss of taste or smell, though this has become less common with newer variants. A diagnostic test, typically a nasal swab, is the only reliable way to confirm which virus you’re dealing with.
How RSV Spreads
RSV travels through respiratory droplets when an infected person coughs or sneezes. It also spreads through direct contact, like kissing a child’s face, or through contaminated surfaces. The virus survives on hard surfaces like countertops for 3 to 30 hours at room temperature. On soft surfaces like clothing or tissues, it lasts less than an hour. On hands, it typically stays infectious for under an hour, but that’s long enough to transfer the virus to a baby’s eyes, nose, or mouth with a single touch.
RSV season in the United States generally runs from fall through spring, with peak activity in December and January in most regions.
Protection for Infants
Two strategies now exist to protect newborns and young infants, who face the highest risk of severe disease.
The first is a protective antibody called nirsevimab, given as a single injection to infants younger than 8 months who are born during or entering their first RSV season. It’s recommended when the mother did not receive an RSV vaccine during pregnancy, when her vaccination status is unknown, or when the infant was born within 14 days of maternal vaccination. Ideally, babies born between October and March receive the shot during their birth hospitalization, though it can be given at any clinic visit. Dosing is weight-based: 50 mg for babies under 11 pounds and 100 mg for those 11 pounds or more.
The second strategy is maternal vaccination. Pfizer’s Abrysvo vaccine is recommended for pregnant women at 32 to 36 weeks of pregnancy during September through January in most of the U.S. The vaccine prompts the mother’s immune system to produce antibodies that cross the placenta, giving the baby protection from birth. In clinical trials, maternal vaccination provided 68% to 72% protection against infant RSV hospitalization. Parents don’t need both strategies. If the mother received the vaccine during the recommended window, the infant typically doesn’t need the antibody injection.
Vaccines for Older Adults
Two RSV vaccines are approved for older adults. Arexvy reduced RSV-related hospitalizations in older adults by 60% to 65%. Abrysvo showed 58% to 63% efficacy in the same population. Both target the protein on the virus’s surface that it uses to enter human cells. Your doctor can help determine whether vaccination makes sense based on your age and overall health.
How RSV Is Diagnosed
Most healthy older children and adults with RSV never get tested because their symptoms resolve on their own. When testing matters, particularly in hospitalized infants or vulnerable adults, two main options exist. Rapid antigen tests deliver results quickly but catch only about 74% of true RSV infections when measured against the gold standard. PCR-based molecular tests are more accurate and have become the preferred method in hospitals. Many clinics now use combination tests that check for RSV, flu, and COVID-19 from a single nasal swab.
Treatment and Recovery
There is no antiviral medication that cures RSV. Treatment focuses on managing symptoms: keeping airways clear with nasal suction for infants, staying hydrated, and using fever reducers as needed. Most children recover in one to two weeks. Hospitalized infants may need supplemental oxygen or, in severe cases, help with breathing until the infection runs its course. The cough can linger for several weeks even after the virus is gone, since the airway lining takes time to regenerate.
For adults, recovery looks similar to bouncing back from a bad cold. Older adults with underlying heart or lung conditions may take longer and face a higher risk of complications like pneumonia. The risk of hospitalization rises sharply after age 75, making prevention through vaccination especially valuable in that age group.