Babies catch RSV (respiratory syncytial virus) the same way they catch most respiratory infections: through droplets that reach their eyes, nose, or mouth. This can happen when someone nearby coughs or sneezes, when a baby touches a contaminated surface and then touches their face, or when a caregiver with the virus on their hands holds, feeds, or kisses them. Nearly all children are infected with RSV at least once by age two, and for most it causes nothing worse than a cold. But for young infants, the virus can be more dangerous because of how small their airways are.
The Main Routes of Infection
RSV travels in tiny respiratory droplets. When an infected person coughs, sneezes, or even talks, those droplets can land directly on a baby’s face or settle onto nearby surfaces. Babies are especially vulnerable to the surface route because they put their hands, toys, and anything else they can grab into their mouths constantly. RSV can survive for many hours on hard surfaces like tables, crib rails, and plastic toys. It lives for shorter periods on soft surfaces like tissues, clothing, and skin, but even a brief window is enough for transfer.
The most common chain of events looks like this: an older sibling or parent picks up the virus, touches their own nose or mouth, then handles a bottle, pacifier, or the baby directly. The virus enters through the baby’s eyes, nose, or mouth. It doesn’t need a dramatic sneeze in the face. Routine caregiving, from wiping a nose to sharing a spoon, provides plenty of opportunity.
Who Passes It to Them
Older siblings are one of the biggest sources of RSV for infants. A school-age child or toddler in daycare may have nothing more than a runny nose and bring the virus home without anyone realizing it’s RSV. Adults can carry and spread it too, often mistaking their symptoms for an ordinary cold. People are typically contagious for three to eight days after symptoms start, though young children and people with weakened immune systems can shed the virus for several weeks.
The incubation period, the gap between exposure and the first symptoms, is usually four to six days. That means a family member who seems perfectly healthy today could already be infectious and not know it yet.
Why RSV Hits Babies Harder
In older children and adults, RSV usually causes mild cold symptoms and resolves on its own. Babies under six months face a different situation. Their airways are physically tiny, so even a small amount of swelling from inflammation can significantly narrow the passages air travels through. When RSV infects the smallest branches of the lungs, it can cause bronchiolitis (swelling of those tiny airways) or pneumonia. That’s why you may hear a baby with RSV wheezing, breathing rapidly, or struggling to feed. Their airways simply don’t have the margin that larger lungs do.
Premature infants, babies with congenital heart conditions, and those with weakened immune systems are at the highest risk for severe illness, but even healthy full-term babies can end up hospitalized if the infection moves deep into the lungs.
When RSV Is Most Likely to Spread
RSV follows a predictable seasonal pattern in the United States. Activity typically rises in October, peaks in December or January, and tapers off by late March. During the 2024-2025 season, the national epidemic began in early November, peaked the week before Christmas, and ended by late March. The percentage of positive tests hit 11% at its peak. This pattern closely matched pre-pandemic years, meaning parents can generally expect the highest risk during the winter holiday season when families gather indoors and older children are mixing at school and daycare.
Geography matters too. Southern regions sometimes see RSV activity start a few weeks earlier than the national average, which can catch families off guard if prevention measures aren’t yet in place.
High-Risk Settings
Daycare centers and childcare facilities are hotspots for RSV transmission. Groups of young children sharing toys, surfaces, and air in enclosed spaces create ideal conditions for the virus to move from child to child. Households with multiple children are similarly risky. Studies consistently show that having an older sibling in school or daycare is one of the strongest predictors of an infant catching RSV in their first winter.
Crowded living spaces, exposure to cigarette smoke (which irritates airways and may make infection more likely to become severe), and frequent visitors during RSV season all increase a baby’s chances of exposure.
How to Reduce the Risk
Basic hygiene makes a real difference. Washing hands thoroughly before touching a baby, keeping obviously sick people at a distance, and regularly cleaning hard surfaces and toys can cut down on transmission. Because RSV survives for hours on hard objects, wiping down crib rails, highchair trays, and countertops with standard household cleaners during RSV season is a practical step. Avoiding kissing a baby on the face when you have any cold symptoms, even mild ones, removes one of the most direct transmission routes.
Immunization Options
Two prevention tools now exist for protecting infants. One is a monoclonal antibody injection given directly to babies, typically before or during their first RSV season. The other is a maternal vaccine given during pregnancy, which allows the mother to pass protective antibodies to the baby before birth. Those maternal antibodies protect the baby for roughly six months after delivery, covering the period when they’re most vulnerable.
Real-world data from the 2024-2025 season shows these tools are working. Among infants under eight months old (the age group eligible for protection), RSV hospitalization rates dropped by an estimated 43% compared to pre-pandemic baseline years. The effect was strongest in the youngest babies: hospitalization rates among infants under three months fell by roughly 45 to 52%, and during peak months the reductions were even larger. In some analyses excluding regions where RSV arrived before prevention products were widely available, the reduction in hospitalizations reached 56 to 71% for the youngest infants.
These numbers don’t mean the virus is gone, but they represent a significant shift. For parents of newborns heading into their first fall and winter, discussing the timing of immunization with a pediatrician well before RSV season starts gives the antibodies time to reach protective levels before the virus begins circulating widely.