Infants with RSV may develop wheezing within 3–4 days after coughing begins

Hong Ju-hee, a pediatric specialist at H Plus Yangji Hospital, explained that infants with RSV may develop lower respiratory tract symptoms, such as rattling from mucus or wheezing, within 3–4 days after coughing begins. She said infants who cannot yet speak have difficulty expressing their symptoms directly.

Respiratory syncytial virus (RSV) initially causes a runny nose, sneezing and a mild fever, making it difficult to distinguish from a common cold. In infants, the infection can rapidly progress to a lower respiratory tract infection, such as bronchiolitis or pneumonia, within days of infection.

Transmission routes include droplets released through coughing and sneezing, as well as close contact involving virus-contaminated hands, toys and household items. In settings such as postpartum care centers, where newborns and mothers stay together and a small number of staff care for multiple newborns, one infected person has a higher likelihood of spreading the virus to several others.

Reinfection with RSV is common, and the infection warrants caution through 24 months of age. Premature infants and infants with underlying conditions such as heart disease, chronic lung disease or weakened immunity face a higher risk of severe illness, while older adults may also develop pneumonia or experience worsening of existing conditions after infection.