RSV is a significant respiratory infection that kills roughly 100,000 children under 5 worldwide each year and up to 10,000 older adults in the United States alone. For most healthy older children and adults, it feels like a bad cold. But for infants, especially those under 6 months, and adults 75 and older, RSV can become a medical emergency requiring hospitalization and intensive care.
Why Infants Are Hit Hardest
RSV starts like any upper respiratory infection, replicating in the nose and throat. Within one to three days, the virus spreads down into the smallest airways in the lungs. There, it damages the cells lining those tiny passages, triggering inflammation, swelling, and a surge of mucus. Dead cells slough off into the already narrowed, mucus-filled airways, creating blockages that trap air and reduce oxygen flow.
The reason this is so dangerous in babies is simple physics: their airways are extremely small. A little bit of swelling and mucus in a newborn’s bronchioles causes proportionally far more obstruction than it would in an adult. This is why RSV is the most common cause of bronchiolitis, the inflammatory condition of the small airways that sends tens of thousands of infants to the hospital each year. Before recent prevention tools became available, roughly 15 out of every 1,000 babies under 8 months old were hospitalized for RSV during a typical season. Globally, RSV causes over 3.6 million hospitalizations in children under 5 every year.
Warning Signs in Babies
RSV typically begins with a runny nose, cough, and mild fever. In most children over age 1, it stays mild. In very young infants, though, the symptoms to watch for look different from what you might expect. Babies under 6 months may become unusually irritable, less active than normal, or start refusing to eat or drink. The most alarming sign is apnea, where the baby pauses breathing for more than 10 seconds.
If your child is breathing fast, visibly working hard to breathe (you can see the skin pulling in between or below the ribs), or is not taking in enough fluids, that warrants emergency medical attention. These signs indicate the airway obstruction has become severe enough that the body is struggling to get adequate oxygen.
RSV in Older Adults
RSV’s reputation as a children’s disease has historically overshadowed its impact on older adults. In the United States, RSV causes up to 160,000 hospitalizations and 10,000 deaths annually among adults over 65. Adults 75 and older face the highest risk, along with those who have chronic heart or lung disease, weakened immune systems, or who live in nursing homes.
RSV can also destabilize conditions you already have. If you’re living with COPD, asthma, or heart failure, an RSV infection can trigger a serious flare that lands you in the hospital even if the infection itself seems moderate. The virus essentially adds enough respiratory stress to push an already compromised system past its tipping point.
RSV Is Often More Severe Than Flu
One useful way to gauge RSV’s seriousness is to compare it to seasonal influenza, a virus most people already respect. Among hospitalized adults in a large study from Spain, RSV patients needed mechanical ventilation at more than double the rate of flu patients (9.3% versus 4.2%). RSV patients also stayed in the hospital about 10% longer on average, 7.7 days compared to 6.8 for flu. In-hospital death rates were similar, around 5%, but when researchers tracked patients for 30 days after discharge, RSV patients had a somewhat higher mortality rate (10.5% versus 8.2% for flu). RSV hospitalizations also cost about 6% more per patient.
These differences matter because they challenge the common perception of RSV as “just another cold virus.” For people in high-risk groups, RSV is at least as dangerous as influenza, and by several measures, it’s worse.
Long-Term Effects on Children
RSV’s consequences don’t always end when the acute illness resolves. Children who experience severe RSV bronchiolitis in infancy face a substantially higher risk of developing asthma later in childhood. In one study following 73 children hospitalized with infant bronchiolitis, 42.5% were still wheezing nearly six years later, compared to just 15% of children who hadn’t been hospitalized. Another study found that RSV bronchiolitis was the single most important risk factor for later asthma, more significant than any other variable studied, though having a family history of allergies or asthma compounded the risk further.
Researchers are still working to understand whether severe RSV directly causes lasting airway changes or whether it reveals a pre-existing vulnerability. Either way, parents of children who had a serious RSV infection should be aware that recurrent wheezing in the following years is common and worth discussing with a pediatrician.
Prevention Has Changed the Picture
The landscape for RSV prevention shifted dramatically starting in 2023 with new tools for both infants and older adults. For babies, a single-dose antibody injection given before or during RSV season reduced RSV hospitalizations by 81% in clinical trials through the first five months after the shot. Real-world data from the 2024-25 season confirmed the impact: hospitalization rates among infants under 8 months dropped by 28% to 56% compared to pre-pandemic seasons, depending on the surveillance network and region.
For older adults, two vaccines now available provide strong protection against RSV-related lower respiratory tract disease. In adults 75 and older, vaccination reduced RSV lung infections by about 69% and cut medically attended RSV illness by roughly 77%. Adults aged 60 to 74 with chronic conditions like heart disease, lung disease, or diabetes saw similar protection, with vaccine efficacy around 73% for both overall and medically attended RSV respiratory disease.
Who Needs to Take RSV Seriously
If you’re a healthy adult between 20 and 60 with no chronic conditions, RSV will almost certainly feel like an unpleasant cold and resolve on its own. The groups who need to treat RSV as a genuinely dangerous infection are specific:
- Infants under 6 months, whose tiny airways are vulnerable to obstruction
- Premature babies and infants with congenital heart or lung conditions
- Adults 75 and older, especially those in nursing homes or long-term care
- Adults of any age with chronic heart failure, COPD, or weakened immune systems
For these groups, RSV is not a minor illness. It fills pediatric ICUs every winter, drives tens of thousands of adult hospitalizations, and carries real mortality risk. The annual economic burden of RSV in U.S. adults over 60 alone is estimated at $6.6 billion. The good news is that effective prevention now exists for the most vulnerable populations, making this the first era in which the most severe outcomes from RSV are largely avoidable.