Respiratory syncytial virus (RSV) causes infections of the lungs and respiratory tract. It's so common that most children have been infected with the virus by age 2. Respiratory syncytial (sin-SISH-ul) virus can also infect adults.
In adults and older, healthy children, RSV symptoms are mild and typically mimic the common cold. Self-care measures are usually all that's needed to relieve any discomfort.
RSV can cause severe infection in some people, especially premature babies, older adults, infants and adults with heart and lung disease, or anyone with a very weak immune system (immunocompromised).