Babies catch RSV (respiratory syncytial virus) the same way they catch most respiratory infections: through their eyes, nose, or mouth. The virus travels in respiratory droplets when someone nearby coughs or sneezes, passes through direct skin-to-skin contact like a kiss on the face, or hitches a ride on contaminated surfaces a baby then touches. For most adults and older kids, RSV feels like a mild cold. For infants, especially those under six months, it can quickly become serious.
The Three Ways RSV Reaches Your Baby
RSV spreads through three main routes, and understanding each one helps explain why the virus is so hard to keep away from young children.
Respiratory droplets. When someone infected with RSV coughs or sneezes, tiny virus-laden droplets land on or near the baby’s face. These droplets enter through the eyes, nose, or mouth. This is the most common transmission route and the hardest to prevent in close quarters, since babies are frequently held face-to-face by caregivers.
Direct contact. Kissing a baby’s face, nuzzling their cheek, or even wiping their nose with an unwashed hand can transfer the virus directly. Adults and older siblings often carry RSV with symptoms mild enough to pass for a regular cold, so they may not realize they’re contagious.
Contaminated surfaces. RSV can survive on hard surfaces like doorknobs, crib rails, and toys. A baby who touches a contaminated surface and then puts their fingers in their mouth or rubs their eyes can pick up the virus. Babies explore everything with their hands and mouths, which makes this route especially relevant.
Why Older Siblings and Caregivers Are the Usual Source
The most common scenario is straightforward: an older sibling brings RSV home from school or daycare. In their body, the virus produces a runny nose and maybe a cough. They feel fine enough to play with the baby, share toys, or sneeze in the same room. The baby’s immune system, still immature and encountering the virus for the first time, has a much harder time fighting it off.
Adults are just as capable of passing RSV along. A parent, grandparent, or visitor with what seems like a minor sniffle can transmit the virus through routine caregiving, holding, or feeding. Because RSV symptoms in adults overlap with the common cold, most carriers never suspect RSV specifically.
When RSV Season Peaks
RSV follows a predictable seasonal pattern in the United States. Activity typically rises in October, peaks in late December, and tapers off by late March. During the 2024-2025 season, positive test results peaked at 11% during the week ending December 21, 2024, and the epidemic window ran from early November through late March. This pattern matched pre-pandemic norms.
For parents of newborns, this means a baby born between October and March enters the world during the highest-risk window. Babies born in late summer or early fall face their first months of life right as RSV circulation ramps up.
What Happens Once the Virus Gets In
After RSV enters through the eyes, nose, or mouth, it infects the cells lining the airways. In older children and adults, the infection stays in the upper respiratory tract, producing cold-like symptoms. In infants, the virus more easily moves into the smaller airways of the lungs. These tiny passages, called bronchioles, swell and fill with mucus, making it progressively harder for the baby to breathe.
Symptoms typically appear four to six days after exposure. Early signs look like a cold: runny nose, decreased appetite, mild cough. Within a day or two, some babies develop wheezing, rapid breathing, or visible effort with each breath (you might notice their nostrils flaring or the skin between their ribs pulling inward). Not every baby progresses to this point, but infants under six months and premature babies are at the highest risk.
How to Reduce Your Baby’s Exposure
Complete avoidance of RSV is unrealistic for most families, but several practical steps lower the odds of transmission. Frequent handwashing before touching the baby is the single most effective measure. Ask anyone who holds your infant to wash their hands first, and keep hand sanitizer accessible for situations where soap isn’t available.
Cleaning frequently touched surfaces, toys, and pacifiers reduces the contaminated-surface route. During peak RSV months, limiting your baby’s exposure to crowded indoor spaces and asking visitors with cold symptoms to wait until they’re well can make a meaningful difference. If an older sibling has a cold, teaching them to cough into their elbow and wash hands often helps, though perfect compliance from a toddler is a tall order.
Immunization Options for Infants
Two forms of immune protection now exist for babies. The first is an antibody shot given directly to the infant. The second is a maternal vaccine given during pregnancy, which passes protective antibodies to the baby before birth.
Antibody Shots for Babies
Infants younger than eight months entering their first RSV season are eligible for an antibody injection if their mother did not receive the RSV vaccine during pregnancy, if her vaccination status is unknown, or if the baby was born within 14 days of the mother’s vaccination. Real-world data show these antibody shots are at least 70% effective at preventing RSV hospitalization. In clinical trials, the efficacy against hospitalization reached approximately 81%.
A second product, approved more recently, showed 91% efficacy against RSV hospitalization through about five months after injection. Some children between 8 and 19 months who face higher risk, including those with chronic lung disease, severe immune deficiency, cystic fibrosis with significant lung involvement, or American Indian and Alaska Native children, are eligible for a dose before their second RSV season.
Maternal Vaccination During Pregnancy
When a pregnant person receives the RSV vaccine, their body produces antibodies that cross the placenta and protect the baby for roughly six months after birth. That six-month window aligns with the period when infants are most vulnerable to severe RSV. If the mother was vaccinated during pregnancy, the baby generally does not need the separate antibody shot.
Why Babies Are More Vulnerable Than Older Kids
Three factors converge to make RSV more dangerous in infancy. First, a baby’s airways are physically tiny. Even modest swelling and mucus production can partially block airflow in passages that are only a few millimeters wide. Second, infants lack prior exposure to RSV, so their immune system has no memory of the virus and mounts a slower, less targeted response. Third, very young babies are obligate nose-breathers, meaning a stuffed nose doesn’t just cause discomfort; it directly interferes with feeding and breathing.
Most healthy infants who catch RSV recover at home within one to two weeks. But roughly 2 to 3% of children under six months with RSV require hospitalization, primarily for supplemental oxygen and hydration when they can’t breathe or feed well enough on their own. Premature babies, infants with heart conditions, and those with weakened immune systems face the highest hospitalization rates.