Respiratory syncytial virus, commonly called RSV, is a highly contagious respiratory virus that infects the lungs and airways. Nearly every child catches it by age two, and adults can be reinfected throughout their lives. For most people it feels like a bad cold, but in infants, older adults, and people with weakened immune systems, RSV can cause serious lung infections that require hospitalization.
How RSV Affects the Airways
RSV targets the cells lining your respiratory tract, from the nose down to the smallest airways in the lungs. Within 18 to 24 hours of infection, the virus begins killing those surface cells, which triggers a cascade of problems. The damaged airway lining swells, and specialized cells ramp up mucus production far beyond normal levels. At the same time, the cells that normally sweep mucus out of the lungs (using tiny hair-like structures called cilia) are replaced by new cells that lack that sweeping ability.
The result is a buildup of mucus, dead cells, and inflammatory debris that physically clogs the smallest airways, called bronchioles. This is why RSV so often leads to bronchiolitis in young children. Their airways are already tiny, so even a small amount of swelling and mucus can partially or fully block airflow. That blockage traps air in parts of the lung, makes breathing harder, and reduces how efficiently oxygen reaches the bloodstream.
Symptoms in Infants and Young Children
RSV symptoms typically appear one to four days after exposure. In babies and toddlers, the first signs are usually a runny nose and decreased appetite, sometimes a day or two before anything else shows up. Coughing develops one to three days later, followed by sneezing, fever, and wheezing.
Very young infants, especially those under six months, may not show the classic cold symptoms at all. Instead, they can become unusually irritable, less active than normal, or have apnea, which means pauses in breathing lasting more than 10 seconds. These breathing pauses are a red flag. If your child is having difficulty breathing, refusing fluids, or their symptoms are getting worse rather than better, that warrants medical attention.
Most children recover in one to two weeks, but the cough can linger. The illness tends to be mildest on the first infection in older children and worst in the very young, premature babies, and children with heart or lung conditions.
Symptoms in Adults
In healthy adults, RSV usually looks and feels like a common cold: congestion, cough, mild fever, fatigue. Many adults with RSV never realize they have anything beyond a typical upper respiratory infection. But adults over 65 and those with chronic heart or lung disease, diabetes, or weakened immune systems are at higher risk for the infection spreading deeper into the lungs, causing pneumonia or worsening existing conditions like COPD or asthma.
How RSV Differs From the Flu and COVID-19
RSV, influenza, and COVID-19 overlap enough in symptoms that you can’t reliably tell them apart without testing. But there are patterns worth knowing. RSV has a short incubation period of one to four days, similar to the flu’s two to three days. COVID-19 can take anywhere from two to 14 days to show symptoms.
RSV tends to produce a narrower set of symptoms: cough, fever, congestion, and reduced appetite. The flu is more likely to bring body aches, chills, headache, and sore throat alongside the respiratory symptoms. COVID-19 shares most flu symptoms but adds some distinctive ones like loss of smell or taste, nausea, vomiting, and diarrhea. RSV’s hallmark is wheezing, particularly in young children, which is less common with flu and COVID.
How RSV Spreads
RSV is transmitted through respiratory droplets when an infected person coughs or sneezes, through direct contact like kissing a child’s face, and by touching contaminated surfaces and then touching your eyes, nose, or mouth. The virus can survive for many hours on hard surfaces like tables, countertops, and crib rails. It doesn’t last as long on soft surfaces like tissues or hands, but long enough for hand-to-face contact to pass it along.
People with RSV are typically contagious for three to eight days, though infants and people with weakened immune systems can spread the virus for up to four weeks. Basic hygiene makes a real difference: frequent handwashing, cleaning high-touch surfaces, and keeping sick family members from close contact with vulnerable people.
Treatment and Recovery
There is no antiviral medication that treats RSV. Care focuses on managing symptoms while the immune system clears the virus. For most children and adults, that means rest, fluids, fever reducers, and saline nasal drops to keep the nose clear. Keeping infants well-hydrated is especially important because congestion makes feeding difficult.
Children who develop more serious breathing problems may need hospital care. In the hospital, treatment centers on keeping oxygen levels adequate and ensuring the child stays hydrated, sometimes through an IV if they can’t drink enough. Most hospitalized children improve within a few days, though some require oxygen support for longer. Antibiotics don’t work against RSV since it’s a virus, and routine use of inhaled medications for wheezing hasn’t shown consistent benefit in infants with bronchiolitis.
Vaccines and Preventive Options
RSV prevention has changed dramatically in recent years. There are now three FDA-licensed RSV vaccines for adults: Arexvy (made by GSK), mResvia (Moderna), and Abrysvo (Pfizer). The CDC recommends a single dose for all adults 75 and older, and for adults 50 to 74 who are at increased risk of severe RSV. Two of these vaccines, Abrysvo and mResvia, are also approved for high-risk adults as young as 18.
For protecting newborns, there are two strategies. Pregnant women can receive Abrysvo between 32 and 36 weeks of pregnancy. The vaccine prompts the mother’s immune system to produce antibodies that cross the placenta and protect the baby during their most vulnerable first months of life. Getting the vaccine after 36 weeks and 6 days isn’t recommended because there isn’t enough time for antibodies to transfer before delivery.
The other option for infants is a monoclonal antibody, a lab-made version of the protective antibodies the immune system would normally produce. This is given directly to the baby and provides protection during RSV season. Your pediatrician can help determine which approach makes sense based on timing and individual circumstances.
How Well Prevention Is Working
Early data on these new prevention tools is encouraging. During the 2024 to 2025 RSV season, hospitalization rates among infants under eight months dropped significantly compared to pre-pandemic baselines. CDC surveillance found cumulative rates of 8.5 per 1,000 children, down from 15.0 per 1,000 in the 2018 to 2020 seasons. The biggest impact was in the youngest babies: hospitalization rates among infants under three months fell by roughly 45 to 52 percent, depending on the surveillance network measured.
These reductions coincide with the rollout of both maternal vaccination and infant monoclonal antibody products, suggesting that widespread uptake of either strategy can meaningfully reduce the burden of severe RSV in the most vulnerable age group.