Avoiding RSV in infancy reduces asthma risk

The RSV virus is harmless for most people, but can cause dangerous symptoms in infants. fizkes / Shutterstock

Respiratory syncytial virus, better known as RSV, is a common virus that infects the lungs and airways. Everyone is infected with RSV during their lives. In most people, infection causes no symptoms or mild ones similar to those of the common cold. Symptoms can include a runny nose, coughing, or wheezing. But RSV can be very dangerous for infants and older adults, who have weaker immune systems. More than 50,000 young children in the U.S. alone are hospitalized with RSV every year.

Infection with RSV at a young age is thought to increase the risk of developing asthma. Asthma is a chronic condition where the airways in the lungs become inflamed and narrowed at times, making it hard to breathe. About 1 in 13 people in the U.S. live with asthma. Most often, it begins in childhood. But studies of the links between RSV infection in infancy and asthma have not been conclusive.

NIH-funded researchers led by Dr. Tina Hartert from Vanderbilt University Medical Center set out to examine this relationship. They enrolled more than 1,900 infants. Recruitment occurred in Tennessee over the course of two years.

The team tracked the children biweekly during the late fall and winter, when RSV is most active, following their birth. If a child’s parent reported symptoms of a respiratory infection, the researchers took a nasal swab to test for RSV. Blood samples were also taken when children were 1 year old to test for RSV antibodies—a sign of previous RSV infection.

The researchers then compared the risk of developing asthma by the age of 5 between children who had and hadn’t been infected with RSV during their first year of life. Results were published on April 19, 2023, in the Lancet.

About 90% of the children had at least one swab or blood sample taken. Of these, 54% had proof of RSV infection during the first year of life.

The researchers tracked almost 1,400 of the children for the full five years of follow up. Overall, 18% developed asthma by the age of 5. The risk of developing asthma differed between kids who had and hadn’t been infected by RSV in their first year of life: 21% of those infected by RSV had asthma by the age of 5, compared with 16% of those who hadn’t had RSV.

This translated to a 26% lower risk of developing asthma by the age of 5 for kids who weren’t infected by RSV in infancy. This reduced risk wasn’t affected by the children’s sex, race or ethnicity, whether or not they attended daycare in infancy, or whether or not their mothers had asthma.

Based on their results, the researchers estimate that about 15% of asthma cases by the age of 5 could be prevented by avoiding RSV infection during infancy. “We believe that when a child is infected with RSV in the first year of life, when the lungs and immune system are still under development, that could lead to certain abnormalities that can later cause asthma,” says lead author Dr. Christian Rosas-Salazar.

The first-ever vaccine against RSV was approved by the Food and Drug Administration for adults over the age of 60 on May 3, 2023. Trials of RSV vaccines and monoclonal antibodies to prevent severe RSV disease in children are still ongoing.

—by Sharon Reynolds