RSV poses serious threat to infants; new vaccines offer protection

Respiratory syncytial virus arrives quietly—a runny nose, a slight cough, fever that comes and goes. For most people, RSV feels like any other cold, something to weather at home with rest and fluids. But for infants, the virus can turn dangerous with startling speed. Each year, RSV sends roughly 3.6 million children under five to the hospital worldwide. About 110,000 of them do not come home.

The virus spreads easily, traveling through the air when an infected person coughs or sneezes, or lingering on surfaces long enough to infect someone who touches them and then their face. Symptoms typically emerge two to eight days after exposure. In older children and adults, the signs are familiar: runny nose, cough, sneeze, fever, sometimes wheezing. In very young infants, the picture is murkier. A baby might simply seem irritable, less active than usual, or begin to struggle for breath—signals that something deeper is wrong.

What makes RSV particularly dangerous in infants is what happens when the virus reaches the lungs. It inflames the small airways, a condition called bronchiolitis, or it settles into lung tissue as pneumonia. These complications can make breathing so difficult that a child needs hospitalization, oxygen support, or in the most severe cases, a ventilator to breathe for them. Certain infants face much higher risk: those born prematurely, babies under six months old, children with chronic lung disease or heart defects, and any child whose immune system is not yet fully formed.

Until recently, parents and doctors had limited options. There is no cure for RSV—no antiviral medication to stop the virus once it takes hold. Treatment means managing symptoms: fever reducers, pain relievers, and in hospital settings, oxygen or intravenous fluids to keep a child stable while their body fights the infection. Antibiotics do not work because RSV is viral, not bacterial. Prevention meant hand-washing, keeping sick people away from infants, and hoping the virus passed by.

That landscape has shifted. Two new tools now exist to prevent severe RSV disease before it starts. The first is a vaccine given to pregnant women during their third trimester. The vaccine triggers the mother's immune system to produce antibodies against RSV, which cross the placenta and enter the baby's bloodstream before birth. When the newborn arrives, they carry these maternal antibodies—a form of passive immunity that shields them during their most vulnerable months, when RSV infection is most likely to turn severe.

The second tool is nirsevimab, a monoclonal antibody administered as a single injection, ideally at birth or as soon as possible afterward. A single dose provides protection for at least five months, spanning the entire RSV season when the virus circulates most widely. For infants who cannot receive the maternal vaccine—perhaps because their mother was not vaccinated during pregnancy—nirsevimab offers a direct line of defense.

These are not incremental improvements. They represent a fundamental shift in how medicine can protect the youngest and most fragile patients from a virus that has killed thousands of children every year. Yet the tools exist only if parents and doctors know about them and choose to use them. The old defenses remain important: frequent hand-washing, keeping newborns away from people who are sick, maintaining clean surfaces. But now those basic practices can work alongside medical interventions that did not exist a year ago.

The question facing families now is not whether protection is possible, but whether they will reach for it. A conversation with a pediatrician about RSV vaccination—for the mother during pregnancy, for the infant after birth—has become as routine as discussing other preventive care. The virus has not changed. But the ability to stop it before it harms a child has.