Respiratory Syncytial Virus (RSV) is a respiratory virus that infects the lungs and breathing passages. It's the most common respiratory virus in infants and young children, infecting virtually every infant by the age of two. In most cases, the virus causes symptoms resembling the common cold and has no long-term impact on your child’s health. In children born prematurely and/or with chronic lung disease, however, the effect of RSV can be severe—even life-threatening. The Synagis Clinic at UCSF Benioff Children's Hospital Oakland provides RSV protection and support for families who need it most.