Respiratory Syncytial Virus (RSV) is a highly common seasonal illness that nearly every child encounters by the age of two. While often presenting as a mild cold in older children and adults, the virus can cause severe respiratory disease in infants. RSV is a leading cause of hospitalization in this age group. This article examines the nature of RSV, the latest statistics on infant mortality, and current medical strategies available to protect vulnerable babies.
What is Respiratory Syncytial Virus?
Respiratory Syncytial Virus is a highly contagious microbe that spreads through direct contact with respiratory droplets, such as when an infected person coughs or sneezes. The virus invades the cells lining the respiratory tract, from the nose down into the lungs. In older, healthy individuals, the infection typically remains in the upper airways, resulting in symptoms similar to a common cold.
When RSV reaches an infant’s lower respiratory tract, it can cause severe inflammation and obstruction of the smallest airways, a condition known as bronchiolitis. This swelling and mucus buildup restrict the flow of air, making breathing difficult and rapid. The infection can also progress to pneumonia, which involves inflammation of the air sacs in the lungs.
Infants have narrower airways and less developed immune systems, making them particularly susceptible to this severe disease. This respiratory distress is why RSV is the leading cause of hospitalization for babies in the United States. Two to three out of every 100 infants under six months old are hospitalized with RSV each year.
The Annual Mortality Rate in Infants
Globally, Respiratory Syncytial Virus is a significant cause of death in young children, responsible for approximately 100,000 deaths annually in children under five years of age. Nearly all of these deaths, about 97%, occur in low- and middle-income countries where access to supportive medical care is severely limited. More than half of all RSV-attributable deaths worldwide occur in infants younger than six months old.
In the United States, the infant mortality rate directly attributed to RSV is much lower. A study examining data from 1999 to 2018 found an average of 28 infant deaths per year were directly coded to RSV. This rate translates to about 6.9 deaths per 1,000,000 live births during that period.
Some researchers suggest the total number of infant deaths associated with RSV may be higher because the virus is often a contributing factor to other causes, such as bronchiolitis. For instance, the same study found an annual average of 80 infant deaths associated with bronchiolitis during that time frame, which is often caused by RSV. The highest RSV-related mortality rates are observed among infants born in December and January, aligning with the typical peak of the RSV season.
Identifying Infants at Highest Risk
While RSV can cause severe illness in any baby, certain populations are at a much higher risk for complications, hospitalization, and death. Age is the strongest risk factor, with infants younger than six months old facing the greatest danger due to their small airways and underdeveloped immune defenses. Infants under two months of age have the most severe outcomes.
Prematurity significantly increases the risk, particularly for infants born before 29 weeks of gestational age, who have substantially higher mortality rates than those born full-term. Babies with chronic lung disease, such as bronchopulmonary dysplasia, also face elevated risk because their respiratory systems are already compromised. Congenital heart defects, especially those involving significant blood flow abnormalities, make it harder for an infant to cope with the increased strain of a respiratory infection.
Infants with weakened immune systems due to underlying medical conditions or treatments are highly susceptible to severe RSV illness. American Indian and Alaska Native children have historically experienced higher rates of severe RSV disease and mortality compared to other populations. Socioeconomic factors, like living in crowded conditions or in regions with limited healthcare access, can also increase the risk of severe illness and death.
Current Strategies for Prevention and Treatment
Preventative measures for RSV have significantly advanced in recent years, offering new ways to protect infants. The most recent and broadly recommended strategy involves the use of nirsevimab, a long-acting monoclonal antibody that provides passive immunity. This single-dose injection protects all infants for an entire RSV season, regardless of their underlying health status.
This newer option is distinct from palivizumab, an older monoclonal antibody reserved only for high-risk infants that required monthly injections during the RSV season. Another major preventative measure is the maternal RSV vaccine, administered to pregnant individuals. This allows protective antibodies to transfer through the placenta to the fetus before birth, providing the newborn with immunity for their first several months of life.
For infants who contract severe RSV, the standard treatment is supportive care administered in a hospital setting. This involves managing symptoms until the infant’s immune system clears the virus. Supportive care includes ensuring proper hydration, managing fever, and providing supplemental oxygen. In the most severe cases, mechanical ventilation may be required to support breathing function.
Parents should seek emergency medical attention if their infant exhibits signs of respiratory distress, such as rapid or shallow breathing, flaring of the nostrils, or a visible pulling in of the chest muscles with each breath. The skin, lips, or nail beds turning blue or gray is a sign of dangerously low oxygen levels and requires immediate care. Early intervention with supportive therapies can significantly improve outcomes for infants with severe RSV.