Respiratory syncytial virus, or RSV, is one of the most common respiratory infections in the world. Most adults experience it as a cold. For infants under 6 months and adults 65 and older, it can cause severe lower respiratory illness requiring hospitalization.
RSV season in the United States typically begins in September, peaks in November and December, and ends by March or April. With school back in session and temperatures dropping, the conditions that drive RSV transmission are assembling now.
What RSV Is and How It Spreads
RSV is a negative-sense, single-stranded RNA virus in the Pneumoviridae family. It infects the cells lining the respiratory tract, producing illness ranging from mild cold symptoms to severe bronchiolitis and pneumonia. The World Health Organization recognizes RSV as one of the leading causes of acute lower respiratory infection in children globally.
The virus spreads through respiratory droplets and direct contact with contaminated surfaces. It can survive on hard surfaces for several hours and on hands for 30 minutes or more. This makes childcare settings, schools, and households with young children particularly efficient transmission environments.
Symptoms: What RSV Looks Like at Different Ages
In older children and adults, RSV presents like a common cold. Symptoms include runny nose, cough, mild sore throat, and low-grade fever. Most people recover without medical intervention in one to two weeks.
In infants under 6 months, RSV can progress to bronchiolitis, an inflammation of the small airways in the lungs. Symptoms of bronchiolitis include rapid or labored breathing, wheezing, flaring of the nostrils, a retracting chest wall (visible pulling in between the ribs during breathing), and poor feeding. Infants with these signs need medical evaluation.
In adults 65 and older and immunocompromised individuals, RSV can cause pneumonia and exacerbate underlying conditions including chronic obstructive pulmonary disease and congestive heart failure.
Fever in RSV is generally mild. A very high fever in a young infant should prompt evaluation regardless of the likely cause.
Prevention: What Is Available in 2026
Three RSV prevention products are now available or recommended in the United States.
Nirsevimab (Beyfortus) for infants. Nirsevimab is a monoclonal antibody, not a vaccine. It provides passive protection against RSV for infants entering their first RSV season. A single dose covers the season. It is recommended for all infants under 8 months born during or entering their first RSV season, and for children aged 8 to 19 months who are at increased risk. Ask your pediatrician about availability before September.
RSV vaccines for older adults. Two RSV vaccines are now available for adults 60 and older: Abrysvo (Pfizer) and mRESVIA (Moderna). Both are single-dose vaccines. The Advisory Committee on Immunization Practices recommends that adults 75 and older, and adults 60 to 74 with risk factors, receive one dose if they have not already. Discuss with your provider whether you qualify.
Vaccination for pregnant women. Abrysvo is also approved for administration during weeks 32 to 36 of pregnancy. Vaccination during pregnancy transfers protection to the newborn through maternal antibodies, covering the highest-risk period before the infant is old enough for nirsevimab.
When RSV Peaks and What Drives the Timing
RSV season start and peak dates vary by geography. Historically, RSV activity begins earliest in the Southeast and Southwest and later in the Northeast and upper Midwest. Nationally, the peak typically falls in November and December.
Post-pandemic RSV patterns have been somewhat unpredictable. During 2020 and 2021, RSV nearly disappeared due to masking and reduced indoor gathering. When restrictions lifted, an out-of-season RSV surge occurred in the summer of 2021, reflecting the immunity debt accumulated in infants who had not been previously exposed. Activity has largely returned to pre-pandemic seasonality since 2022, though earlier starts in some regions remain a pattern worth watching.
Difference Between RSV, Influenza, and COVID-19
All three viruses circulate simultaneously in fall and winter and share overlapping symptoms. A few distinctions are useful in practice.
RSV in infants often produces prominent wheezing that is less common with influenza. Influenza typically produces higher fever and more significant body aches than RSV. COVID-19 can produce loss of taste and smell, which is uncommon with RSV or influenza. None of these distinctions is reliable enough for clinical diagnosis without testing. Rapid antigen tests for influenza and COVID are widely available; RSV testing is more commonly done in clinical settings for hospitalized infants.
Track RSV Activity Near You
Virus Watcher tracks RSV and acute bronchiolitis activity across the United States, integrating emergency department data, wastewater signals, and clinical surveillance reports. Alerts can be set for your state so you know when local activity is rising.
Check current activity in your state:
