RSV is the leading cause of hospitalization in infants under one year old, and yes, it can be dangerous, especially for babies younger than six months. Globally, RSV causes over 3.6 million hospitalizations and roughly 100,000 deaths in children under five each year, with about half of those deaths occurring in infants under six months. For most healthy babies, RSV will look and feel like a bad cold. But for some, it progresses into a lower respiratory infection that makes breathing genuinely difficult.
Why Babies Are More Vulnerable
Two things work against infants when RSV hits: tiny airways and an immature immune system. An adult’s airways can swell and produce extra mucus during a respiratory infection without much trouble breathing. A baby’s airways are so narrow that even a small amount of swelling or mucus can partially block airflow. RSV triggers inflammation, destroys cells lining the airways, and ramps up mucus production. In a baby, that combination can obstruct breathing in a way it simply wouldn’t in an older child or adult.
Their immune systems compound the problem. Babies under six months haven’t had time to build effective immune responses to respiratory viruses. The immune reaction they do mount can be excessive and poorly targeted, causing more inflammation and tissue damage than necessary. This is why the youngest infants tend to get the sickest.
How RSV Differs From a Regular Cold
RSV often starts looking exactly like a cold: runny nose, mild cough, maybe a low fever. In many babies, it stays that way and clears up on its own. The concern is when the virus moves from the upper airways (nose and throat) into the lower airways (the small breathing tubes in the lungs), causing bronchiolitis. That’s when symptoms shift from “bad cold” to something more serious.
Signs that RSV has moved into the lungs include fast breathing, wheezing, and visible effort to breathe. You might notice your baby’s nostrils flaring with each breath, their head bobbing, or rhythmic grunting. One of the most reliable signs is chest wall retractions: watch your baby’s rib cage as they inhale, and if you see the skin pulling inward between the ribs or under the neck, forming a visible “V” shape, they’re working much harder than normal to get air in.
In very young infants under six months, the signs can be subtler and easier to miss. Instead of dramatic coughing or wheezing, the baby may simply become unusually irritable, less active, or refuse to eat. One particularly concerning symptom in this age group is apnea, which means pauses in breathing lasting longer than 10 seconds.
The Illness Timeline
RSV infections typically last one to two weeks total. Symptoms usually start mild and worsen over the first several days, with days three through five often being the hardest. This is when breathing difficulties are most likely to appear and when hospitalizations tend to happen. After the peak, most babies gradually improve, though a lingering cough can stick around for a couple of weeks. Knowing that the illness gets worse before it gets better is important, because a baby who seems fine on day one or two may need closer watching over the next few days.
Which Babies Face the Highest Risk
Any infant can develop a serious RSV infection, but certain groups face significantly higher odds of complications:
- Premature babies, whose lungs and immune systems had less time to develop before birth
- Babies with congenital heart or lung conditions, who already have compromised respiratory function
- Infants with weakened immune systems, whether from a medical condition or treatment
- Babies with neuromuscular disorders, particularly those who have difficulty swallowing or clearing mucus on their own
- Children with severe cystic fibrosis
Even among otherwise healthy babies, those under two to three months old are at disproportionate risk simply because of how small their airways are and how new their immune systems are.
Hospitalization and Mortality Numbers
Before newer preventive treatments became available, roughly 15 out of every 1,000 infants under eight months old were hospitalized for RSV in a typical season in the United States. For the youngest babies, those under three months, the rate was even higher. During the 2024-25 season, after new immunizations became widely available, hospitalization rates dropped to about 8.5 to 10.7 per 1,000 for infants under eight months, a meaningful reduction but still a substantial number of sick babies.
Most hospitalized infants recover fully. Death from RSV in the United States is uncommon in infants who receive modern medical care, but it does happen, and it’s far more common in low-resource settings. The World Health Organization estimates that approximately 50,000 children under six months die from RSV globally each year.
The Link to Childhood Asthma
Severe RSV in infancy doesn’t just cause short-term problems. Six decades of research have consistently shown a connection between RSV bronchiolitis and later childhood asthma. A large U.S. birth cohort study (known as INSPIRE) found that infants who avoided RSV infection during their first year of life had a 26% lower risk of having asthma at age five compared to those who were infected. The researchers estimated that about 15% of asthma cases in five-year-olds could theoretically be prevented if RSV infection during infancy were avoided entirely. This doesn’t mean every baby who gets RSV will develop asthma, but severe infections do appear to leave a lasting mark on developing lungs.
Prevention Options Available Now
Two newer tools have changed RSV prevention for infants significantly. The first is nirsevimab, a single-dose antibody injection given directly to the baby, typically shortly after birth or at the start of RSV season. CDC data shows it is 90% effective at preventing RSV-related hospitalization during a baby’s first RSV season. Unlike a traditional vaccine, it provides ready-made antibodies rather than asking the baby’s immune system to produce its own.
The second option is a maternal vaccine given during pregnancy. When a pregnant person receives this vaccine, their body produces antibodies that cross the placenta and protect the newborn for approximately six months after birth, covering the window when babies are most vulnerable. The two approaches serve the same purpose, so most infants receive one or the other rather than both.
Since these products became widely available, hospitalization rates for the youngest infants (under three months) have dropped by roughly 45 to 52%, with some surveillance sites reporting reductions as high as 71%. These are among the largest single-season improvements in RSV outcomes ever recorded in infants.
What to Watch For at Home
If your baby has cold symptoms during RSV season (typically fall through early spring), keep a close eye on their breathing and feeding. A baby who is still eating well and breathing comfortably is generally handling the infection fine, even if they’re congested and fussy. The warning signs that things are progressing include difficulty breathing, visible rib or neck retractions, wheezing, refusal to eat or drink, pauses in breathing, and any change in skin color toward pale, gray, or bluish tones around the lips or nail beds. These signs call for prompt medical evaluation, not a wait-and-see approach.
Keeping your baby hydrated is the single most important thing you can do at home. Smaller, more frequent feedings often work better than regular-sized ones when a baby is congested. A bulb syringe or nasal aspirator to clear mucus before feedings can help, since babies breathe primarily through their noses.